bluuebunny/crossref_metadata_2025 huggingface dataset:
THE DISTRIBUTION OF DICTYOSTELID CELLULAR SLIME MOLDS IN SOUTHERN CALIFORNIA WITH TAXONOMIC NOTES ON SELECTED SPECIES
Authors: Benson Manetta R. , Mahoney Daniel P.
Published: January 2018

The occurrence and distribution of Dictyostelid cellular slime molds in southern California were investigated by means of a clonal isolation technique that permitted quantitative sampling of populations. Thirteen species were isolated. These include (in approximate order of decreasing frequency): Dictyostelium rosarium Raper and Cavender, D. mucoroides Brefeld, D. sphaerocephalum (Oud.) Sacc. and March., D. aureum Olive, Polysphondylium pallidum Olive, D. minutum Raper, D. giganteum Singh, D. purpureum Olive, P. violaceum Brefeld, D. mucoroides variant, Acytostelium leptosomum Raper and Quinlan, D. polycephalum Raper, and a new species of Dictyostelium. D. rosarium and D. aureum, both rarely reported in the literature, were common and widespread. Trends in habitat preference of the Dictyostelids encountered are discussed. Selected taxonomic details are provided for D. rosarium, D. aureum and members of the “D. mucoroides complex“—D. mucoroides, D. sphaerocephalum, D. giganteum, and a D. mucoroides variant.
THE VASCULAR SYSTEM OF THE INFLORESCENCE AXIS OF ANDROPOGON GERARDII (GRAMINEAE) AND ITS BEARING ON CONCEPTS OF MONOCOTYLEDON VASCULAR TISSUE
Authors: Maze Jack
Published: January 2018

The vascular bundles in the inflorescence axis of Andropogon gerardii occur in inner and outer systems. The inner system is made up of large, early developing strands that, at earliest stages of development, are precocious (= the appendage they are to serve has not yet been initiated). The outer system consists of later developing smaller strands that are open ended in a proximal direction (= strands differentiate basipetally in the cortex below the appendage they serve). Bundles of both the inner and outer systems are not connected to other procambium early in their development but exist as isolated strands. The veins of the inner system of the inflorescence axis occur as sympodia. The presence of inner and outer systems in the vascular tissue is common to most monocotyledons. However, amongst monocotyledons, only certain grasses have been shown to have strands of the inner system that are isolated early in development. Many dicotyledons have large strands which are precocious and some have smaller, later developing strands which are open ended in a proximal direction, hence they occur as isolated strands. These smaller strands in dicotyledons occur between large strands. Certain dicotyledons have an inner and an outer system of veins. Of these, some have veins of the inner system that differ from the inner system bundles of monocotyledons in that they also form part of the outer system of veins, or develop at a different time. One other dicotyledon with an inner and outer system, Bougainvillea, differs from monocotyledons only in that the bundles of the outer system do not seem to be isolated early in their development and anastomoses are seen between the inner and outer systems. Thus, it appears that monocotyledons differ from dicotyledons only in the presence of independent inner and outer systems of vascular bundles in the former. Thus, the hypothesis of Zimmermann and Tomlinson that there are basic differences between monocotyledon and dicotyledon vascular systems is not substantiated. It is even suspected that monocotyledon and dicotyledon vascular systems will be demonstrated to be modifications of a basic plan consisting of large, acropetally differentiating and smaller, basipetally differentiating strands.
PHENOLOGY AND REPRODUCTIVE ALLOCATION IN ANDROPOGON SCOPARIUS (GRAMINEAE) POPULATIONS IN COMMUNITIES OF DIFFERENT SUCCESSIONAL STAGES
Authors: Roos Frederick H. , Quinn James A.
Published: January 2018

Successional populations of Andropogon scoparius in Franklin Township, Somerset County, New Jersey, were compared as to their phenology and reproductive allocation. Field data from six populations in old‐fields ranging in age from 2 to 40 years indicated significant differences in both phenology and reproductive effort (ratio of reproductive to total shoot biomass). Mean date of first anthesis was consistently later with increasing age of the old‐field, and the later the first anthesis date for a population, the lower was the reproductive effort. Population data on mean maximum height and seed weight showed no relation to successional age. Greenhouse experiments on three of the populations revealed that most of the field differences were attributable to local habitat effects on phenotypic expression. The possibility of some genetic differentiation paralleling successional age was raised by the consistent (though sometimes statistically not significant) differences between the early (3‐yr) and late (40‐yr) successional populations in date of first anthesis and in reproductive effort under two light intensities and uniform greenhouse conditions.
ADVENTIVE EMBRYOGENESIS IN CITRUS AND ITS RELATION TO POLLINATION AND FERTILIZATION
Authors: Esen Asim , Soost Robert K.
Published: January 2018

Cytological and histological studies of seeds from three facultative apomictic Citrus cultivars show that adventive embryos develop, as a rule, from the first few cell layers of the nucellus adjacent to the embryo sac in the micropylar half and occasionally from the chalazal end. The adventive embryos initiated in nucellar tissue away from the embryo sac and most of those initiated from the chalazal end of the nucellus do not develop beyond the one‐celled stage. When two or more embryos are developing in the same seed, the successful development of a given embryo depends on its location in relation to access to nutrients from the endosperm. The presence of a zygote and triploid endosperm in seeds with adventive embryos, the abortion of seed when endosperm degenerates, and the lack of seed set without pollination indicate that pollination and fertilization are essential for in vivo adventive embryogenesis.
SOME FINE STRUCTURAL OBSERVATIONS ON DEVELOPING AND MATURE SIEVE ELEMENTS IN THE BROWN ALGA LAMINARIA SACCHARINA
Authors: Sideman Eric J. , Scheirer Daniel C.
Published: January 2018

The differentiation of sieve elements from inner cortical cells of the stipe of Laminaria saccharina (L.) Lamour. involves the development of a well‐structured protoplast and an end wall possessing evenly spaced pores which are visualized by electron microscopy. The protoplast consists of organelles which are commonly found in brown algal cells, including nuclei, cup‐ or horseshoe‐shaped chloroplasts, dictyosomes, mitochondria, and ER. Mitochondria and clusters of small vacuoles, presumably redistributed by the surging effect which occurs in sieve elements, were routinely observed in the vicinity of the end wall. Chloroplasts were seen in progressively degenerated states in older sieve elements, yet nuclei were determined to be non‐necrotic. Numerous pores along the end walls interconnect adjacent sieve elements. Each pore is traversed by a strand of cytoplasm and surrounded by plasmalemma. The pores are open and possess no callose. In this paper the sieve element ultrastructures of L. saccharina are compared to those in L. groenlandica, Alaria marginata, Nereocystis lutkeana and Macrocystis pyrifera, and a possible phylogenetic specialization of sieve elements is presented in table form and discussed.
POPULATION STUDIES AMONG SONORAN DESERT SPECIES OF PARMELIA SUBG. XANTHOPARMELIA (PARMELIACEAE)
Authors: Nash Thomas H. , Zavada Michael
Published: January 2018

Species of Parmelia subg. Xanthoparmelia exhibit partial morphological convergence in a region of sympatry in the northern portion of the Sonoran Desert. Within the isidiate morph of the population, chemotypic variation is present. These chemotypes exhibit habitat selection among different rock substrates within a region of relatively uniform climate and topography. Partial habitat selection is also demonstrable for the chemotypes of the nonisidiate morph in the population. Other morphological characters are useful in segregating portions of the isidiate and nonisidiate morphs into chemically distinct groups that have previously been assumed to represent only chemotypic variation.
ENDOMITOSIS IN TAPETAL CELLS OF EREMURUS (LILIACEAE)
Authors: Oksala Tarvo , Therman Eeva
Published: January 2018

True endomitosis in the anther tapetum of the liliaceous plant Eremurus is described. The nuclear membrane does not disappear, but during metaphase the chromosomes are condensed, often considerably more than in normal mitosis. When the pollen mother cells (PMCs) go through the last premeiotic mitosis, the tapetal cells have one diploid nucleus which divides while the cell remains undivided. The two diploid nuclei may undergo an endomitosis and the resulting tetraploid nuclei a second endomitosis. An alternative pathway is an ordinary mitosis—again without cell division—instead of one of the endomitotic cycles. The cytological picture in the tapetum is further complicated by restitution in anaphase and fusion of metaphase and anaphase groups during mitosis, processes which could give rise to cells with one, two, or three nuclei, instead of the expected two or four. No sign of the so‐called “inhibited” mitosis is seen in these tapetal cells. When the PMCs are in leptotene‐zygotene, very few tapetal nuclei are in endomitosis. When the PMCs have reached diplotene, almost 100% of cells which are not in interphase show an endomitotic stage.
SEED AND VEGETATIVE REPRODUCTION IN RELATION TO DENSITY IN FRAGARIA VIRGINIANA (ROSACEAE)
Authors: Holler Linda C. , Abrahamson Warren G.
Published: January 2018

Transplants of Fragaria virginiana Duchesne, the wild strawberry, from field and woods sites, were studied under controlled laboratory conditions to determine their seed and vegetative reproduction responses under different density conditions. The following results were obtained: (1) Increased competition among high density grown plants resulted in lower total biomass when compared to low density grown plants; (2) Increased shading in high density plots resulted in a greater percentage of biomass in leaves; (3) The percentage of total biomass in reproductive organs (seed and vegetative) was higher in low density grown plants; (4) Vegetative “reproductive effort” was higher in low density plots than in high density plots while seed “reproductive effort” remained constant between the two density treatments; (5) No significant difference between plants from habitats of different successional maturity was observed under the experimental treatments. These results are discussed in relation to reproductive density response models.
FINE STRUCTURE OF THE DORMANT EMBRYO OF MEDICAGO SATIVA
Authors: Singh A. P.
Published: January 2018

The subcellular organization of epidermal and parenchymatous cells of various embryo parts of naturally desiccated Medicago sativa seeds was examined by electron microscopy. Both epidermal and parenchymatous cells were filled with reserve protein and lipid bodies, which varied somewhat in structure, size, and abundance among different embryo parts and between epidermal and cortical cells of the same part. Variations in wall thickness, nuclear conformation, and clarity of organelle membranes were noted. Mitochondria and plastids were recognizable but were poorly differentiated. The endoplasmic reticulum was sparse and not well defined, microtubules were rarely encountered, while dictyosomes appeared to be absent. Polyribosomic configurations were lacking although the cytoplasm of most cells contained large concentrations of ribosomes.
OVULE ONTOGENY, MEGASPOROGENESIS, AND EARLY GAMETOGENESIS IN TRIFOLIUM REPENS (PAPILIONACEAE)
Authors: Rembert David H.
Published: January 2018

To aid in understanding of the early events in seed development, surface topography observations with the scanning electron microscope can be coupled with new methods of clearing tissues for light microscopy study. These techniques reveal that two to four ovules begin development along the placental ridge as conduplication of the carpel proceeds in Trifolium repens L. A multicellular archesporium may develop giving rise to several sporogenous cells and ultimately to more than one megasporocyte. However, meiosis is completed in only one megasporocyte to give rise to a single linear tetrad of megaspores. The chalazal megaspore functions in megagametogenesis. Megasporogenesis and megagametogenesis progress as ovule ontogeny proceeds. The outer integument develops more rapidly than the inner and contributes to the final form of the campylotropous ovule. The most dramatic change in ovule form occurs as the tetrad develops and the functional spore enlarges and divides mitotically to produce the two‐nucleate megagametophyte. It can be demonstrated that this early gametophyte develops faster than it is allowed to expand in the nucellar mass. This may in part explain why there is gametophyte failure and reduced seed set in clovers.
ON THE STEM APEX, LEAF INITIATION AND EARLY LEAF ONTOGENY IN FILICALEAN FERNS
Authors: Bierhorst David W.
Published: January 2018

A general account of the stem apex organization in ferns is presented in support of the classical single apical cell concept. The range in variation of apical cells and of their modes of division are described. Evidence is brought out to indicate probable directing effects of the apical cell on modes of division of surrounding cells and on the leaf mother cell. Initiation of and eventual establishment of a stabilized apex in fern leaves is described. Of the more than 50 genera studied, the leaves of all are traceable to a single mother cell from which the leaf apical cell is cut out. Apical dichotomies are described in a number of genera as well as their effect on early leaf development. Results are discussed in a phylogenetic and morphogenetic context of leaf appendicularization.
THE EFFECTS OF RELATIVE HUMIDITY AT THE TIME OF FLOWERING ON FRUIT SET IN BEAR OAK (QUERCUS ILICIFOLIA)
Authors: Wolgast Leonard J. , Stout Benjamin B.
Published: January 2018

Fifty‐six randomly selected bear oak trees were moved into growth chambers to determine the influence of relative humidity at the time of flowering on fruit set. The effect of humidity greater than 61 % was to greatly reduce fruit set. Trees which were kept in a chamber where relative humidity was less than 50 % had significantly higher fruit set.
ACAULANGIUM GEN. N., A FERTILE MARATTIALEAN FROM THE UPPER PENNSYLVANIAN OF ILLINOIS
Authors: Millay Michael A.
Published: January 2018

Material described by Graham as Cyathotrachus bulbaceus is believed to represent a new genus that is a common constituent of Upper Pennsylvanian coal balls. The sessile synangia of Acaulangium gen. n. are borne in a row on either side of the pinnule midrib and are composed of four to six short, tapering, laterally appressed sporangia. The sporangia have extended tips which curve over the inside of the synangium distally and delimit a small open area inside the synangium. The outer facing walls of the sporangia are two to three cells thick throughout while the inner facing walls are uniseriate. During dehiscence the sporangia separate laterally and spore release results from the rupture of a row of elongate cells along the inner sporangium midline. Among species of Scolecopteris the new genus resembles S. illinoensis and S. minor var. parvifolia but differs in its sessile synangial attachment. The additional parenchyma present between sporangial cavities in the synangia of Acaulangium, and the tendency toward bilateral symmetry suggests an early stage in the evolution of a bivalve synangium such as is present in Marattia.
IDENTIFICATION AND PHYLOGENETIC IMPLICATIONS OF FATTY ACIDS AND STEROLS IN THREE GENERA OF AQUATIC PHYCOMYCETES
Authors: Southall Margaret Ann , Motta Jerome J. , Patterson Glenn W.
Published: January 2018

Allomyces macrogynus, A. arbuscula, A. javanicus, Allomyces male and female hybrid strains, Blastocladia ramosa and Monoblepharella sp. were examined for their fatty acid and sterol compositions by GLC and combined GLC/MS. All the organisms produce a range of fatty acids 12 to 20 carbon atoms in length. Palmitic, stearic, and arachidic acid represent the highest concentrations of saturated fatty acids; oleic, linoleic, and arachidonic acid the highest unsaturated fatty acids. B. ramosa synthesizes only two polyunsaturates, linoleic and linolenic, but Allomyces and Monoblepharella are capable of desaturation as far as arachidonic acid. Cholesterol is produced by all the isolates and is the dominant sterol in Allomyces. 24‐Methyl and 24‐ethyl derivatives of cholesterol are the dominant sterols of Monoblepharella. B. ramosa contains a more complex sterol mixture representing changes which occur in the formation of cholesterol from lanosterol: 24‐dihydrolanosterol, 14α‐methyl Δ8‐cholestenol, Δ8(9)‐cholestenol, 14α‐methyl Δ7‐cholestenol, Δ7‐cholestenol and cholesterol. Δ7‐cholestenol, 24‐dihydrolanosterol, and 14α‐methyl Δ8‐choIestenol appear to be the major components. This is the first time that 14α‐methyl Δ8 and 14α‐methyl Δ7‐cholestenol have been reported as naturally occurring sterols.
AN S.E.M. SURVEY OF THE FIVE CARNIVOROUS PITCHER PLANT GENERA
Authors: Adams Richard M. , Smith George W.
Published: January 2018

Scanning electron microscopy was used to observe features of representative species of the five carnivorous pitcher plant genera which allow them to lure, capture, and digest insects. Nepenthes rafflesiana, Sarracenia purpurea, Darlingtonia californica, Heliamphora heterodoxa, and Cephalotus follicularis were studied. The many morphological similarities observed in the phylogenetically unrelated plants show evidence supporting the concept of their convergent evolution. Several previously undescribed features of some plants were resolved which help elucidate their insect trapping mechanisms.
A GENETIC SYNDROME AFFECTING LEAF DEVELOPMENT IN PISUM
Authors: Marx G. A.
Published: January 2018

A recessive foliage mutant of Pisum, designated ‘sinuate leaf’ (sil), was found to have two distinct forms of expression, depending on the background genotype. In an af/af background—wherein leaflets are converted to tendrils—sil/sil plants had adventitious tendrils arising from clefts in the distal portion of the stipule. These adventitious tendrils were morphologically modified, just as were the true tendrils on the same plant, by different allelic combinations at the tl locus. In the standard Af background, sil/sil plants had neither incised stipules nor adventitious tendrils, although they did have undulated and somewhat distorted leaflets and stipules. Because mutant expression was variable in an Af background, classification of segregating populations was uncertain. This uncertainty was removed by taking advantange of pleiotropic effects exerted by sil in the presence of one of the wax mutants, wlo, wb, or wsp. Homozygous wlo plants ordinarily have uniformly waxy stipule surfaces, but when the plants were also homozygous for sil the stipule tips were waxless. Conversely, wb/wb and wsp/wsp plants ordinarily have uniformly waxless stipules, but when wb/wb or wsp/wsp plants were also homozygous recessive for sil the stipule tips were waxy. However, sil had no observable effects of any kind on the stipule tips of plants with stipules reduced in size by the action of st/st. By their individual and combined effects, the foliage mutants used in this study revealed developmental relationships among leaf parts not otherwise evident in non‐mutant plants.
SEXUAL AND GENETIC ISOLATION IN THE COSMOPOLITAN ALGAL SPECIES PANDORINA MORUM
Authors: Coleman Annette Wilbois
Published: January 2018

In an effort to analyze the nature of a taxonomic species in the microalgae, the major biological characters of various isolates ofPandorina morumhave been studied. Seventy heterothallic clones from 31 collecting sites on three continents were found to represent 20 reproductively isolated groups, based on their ability to form zygotes when paired in all possible combinations. Successful germination of the zygotes and demonstrated fertility of their products suggest that each reproductively isolated group represents a syngen—a group of organisms sharing a common gene pool. A further indication of the close relationship of members of the same syngen is that its representatives all share a common chromosome number, time of division, and zygote distribution pattern, characters which vary between syngens. The known range of 18 of the syngens is less than 500 km. The other two syngens may have a world‐wide distribution; they both have a haploid chromosome number of 5. Crosses between geographically isolated clones in these two syngens and one other give evidence of both pre‐ and postzygotic partial isolation within a syngen. Analysis of collections from two revisited sites demonstrated that representatives of a syngen can be recovered after 19 years have elapsed, and that a single pond may contain as many as four syngens. The results obtained forP. morumare compared with the information available on other microalgae with a similar breeding system, and the possible causes and consequences of the species structure are discussed.
HYBRIDIZATION BETWEEN ASTER AND MACHAERANTHERA AND ITS TAXONOMIC SIGNIFICANCE
Authors: Stucky Jon
Published: January 2018

A controlled crossing program resulted in the production of four interspecific and three intergeneric hybrids among species of Aster sect. Oxytripolium and Machaeranthera. Meiotic analysis revealed stronger degrees of genome homology in some of the intergeneric hybrids than in some of the interspecific hybrids. The significance of these results to the taxonomy of Aster and Machaeranthera was considered and the result was the transfer of Aster sonorae to Machaeranthera.
FURTHER OBSERVATIONS ON THE DIFFERENTIAL SENSITIVITIES TO PLANT GROWTH REGULATORS BY CULTURED “SINGLE” AND “DOUBLE” FLOWER BUDS OF NIGELLA DAMASCENA L. (RANUNCULACEAE)
Authors: Raman K. , Greyson R. I.
Published: January 2018

In Nigella damascena, where “doubleness” behaves as a single gene character, recessive to the normal wild “single” form, we detected a number of differential responses of cultured floral apices of the two forms to plant growth regulators. “Single” buds initiated all organ types on a defined medium lacking any plant growth regulators. “Double” buds, however, required either kinetin or GA3 for the development of a normal organ complement. Kinetin enhanced the growth and development of buds of both genotypes, whereas GA3, at all concentrations, specifically inhibited the initiation and growth of stamens and nectaries in “single” buds. No combination of IAA or kinetin overcame this inhibition of “single” buds by GA3. In the presence of both IAA and GA3, “single” buds, following the initiation of normal carpels, initiated a few abnormal carpelloid structures from regions which had failed to produce stamens and nectaries. These observations, coupled with other studies including those on the endogenous levels of gibberellin in the two genotypes, suggest that “doubleness” correlates strongly with a modification of gibberellin metabolism. The causal connection between the two phenomena is as yet to be discovered.
ULTRASTRUCTURE OF GLANDULAR TRICHOMES OF LEAVES OF NICOTIANA TABACUM L., cv XANTHI
Authors: Akers Carolyn P. , Weybrew J. A. , Long R. C.
Published: January 2018

Electron microscopy confirms previous light microscope observations that tobacco leaf trichomes are glandular and that there are two different types. Both the tall trichome (multicellular stalk, unicellular or multicellular head) and the short trichome (unicellular stalk; multicellular head) exhibit characteristics common to gland cells—a dense cytoplasm, numerous mitochondria, and little vacuolation. The tall trichome contains structurally well developed chloroplasts and an elaborate network of endoplasmic reticulum. The short trichome contains undifferentiated plastids and endoplasmic reticulum which parallels the nucleus and plasmalemma. Few dictyosomes are seen either in the short trichome or in the tall trichome. The short trichome appears to undergo structural changes concurrently with the appearance of secretory product within the cells. The most noticeable change is the formation of the extraplasmic space between the cell wall and the plasmalemma. Electron dense secretory product is observed between the plasmalemma and the cell wall and within the intercellular spaces.
TYPES OF LATICIFERS AND CRYSTALS IN JATROPHA AND THEIR TAXONOMIC IMPLICATIONS
Authors: Dehgan Bijan , Craig Mary E.
Published: January 2018

Anatomical examination of 37 species of Jatropha (Euphorbiaceae) has revealed the occurrence of two distinct types of laticifers—articulated, and nonarticulated—in addition to idioblasts that are irregularly shaped individual cells. With the notable exception of J. augustii Pax & K. Hoffm. (section Peltatae (Pax) Dehgan & Webster), these idioblasts occur in the two most advanced sections of the subgenus Curcas (Adans.) Pax, namely Loureira (Cav.) Muell. Arg. ex Pax and Mozinna (Ortega) Pax. The presence of two laticifer types and “idioblastic laticifers” in the genus, in association with the morphological reduction series found with evolutionary advancement are, therefore, significant in the delimitation of sections and subsections. Further evidence is presented by the occurrence of “chambered crystalliferous cells” in subgenus Curcas, but not in subgenus Jatropha (=Adenorhopium Griseb.). Reexamination of laticifers in other genera of the Euphorbiaceae is suggested as a possible means of alleviating the long‐standing taxonomic dilemma of this large and morphologically diverse family.
STUDIES IN THE BIGNONIACEAE. II. ONTOGENY OF DIMORPHIC ANTHER TAPETUM IN TECOMA
Authors: Nanda Kanan , Gupta Shrish C.
Published: January 2018

A developmental study of anther tapetum in Tecoma stans has shown that the hypodermal archesporial layer differentiates in each microsporangium by cutting off a primary parietal layer to the outside (epidermal) and a primary sporogenous layer to the inside (connective). The primary parietal layer divides periclinally, producing the outer secondary parietal layer, which by further divisions, forms the future endothecium and the middle layer. On epidermal side, the inner secondary parietal layer gives rise to tapetum. The remainder of the tapetum on the inside (connective) is contributed by the parenchymatous connective cells lying just outside the sporogenous cells. The tapetum thus follows the dicotyledonous type of ontogeny. It also shows a distinct dual origin and is structurally dimorphic.
THE POLLINATION ECOLOGY OF AQUILEGIA ELEGANTULA AND A. CAERULEA (RANUNCULACEAE) IN COLORADO
Authors: Miller Russell B.
Published: January 2018

Aquilegia elegantula Greene and A. caerulea James occur in montane and subalpine habitats in the southern Rocky Mountains of western North America. The red and yellow flowers of A. elegantula are nodding, odorless, protogynous, and secrete a concentrated (44%) sucrose nectar in the floral spurs. Seed set in flowers under pollinator exclosures was 12% while seed set in open‐pollinated flowers was 65%. The flowers of A. elegantula are pollinated primarily by the Broad‐tailed Hummingbird (Selasphorus platycercus [Swainson]) and by at least three species of pollen‐foraging bumblebees, of which Bombus occidentalis Greene is the most common. The blue and white flowers of A. caerulea are erect, mildly fragrant, protandrous, and secrete a 26% sucrose nectar. Seed set in caged flowers in the field averaged 39%. in uncaged flowers 54%. The most important pollinators of A. caerulea are the crepuscular hawkmoth, Hyles (=Celerio) lineata (Fabricius) and ten species of pollen‐foraging Bombus. The most abundant bumblebee species, B. occidentalis, is also a frequent nectar thief. Differences in pollination systems alone probably do not constitute an effective anti‐hydridization mechanism between A. elegantula and A. caerulea, but do serve to reinforce differences in habitat and flowering time that distinguish the two species.
TURION FORMATION AND GERMINATION IN SPIRODELA POLYRHIZA
Authors: Newton R. J. , Shelton D. R. , Disharoon S. , Duffey J. E.
Published: January 2018

Three clones of Spirodela polyrhiza L. (Schleid.) formed dormant bodies called turions. A clone from Puerto Rico did not form turions under all conditions tried. In those clones producing turions, formation was stimulated by the addition of sucrose (10–50 mM) to the nutrient solution. Increased levels of Ca(NO3)2 plus sucrose stimulated turion production. In the absence of NO3–, Ca++ was more effective than K+ in stimulating turion formation. Turion buoyancy was not light dependent, nor was it promoted by sucrose. Normal turions required light for germination, whereas sucrose‐induced turions germinated in the dark. Dark germination was not promoted by either Ca++ or K+. Sucrose stimulation of turion formation and subsequent promotion of dark germination was attributed to metabolic rather than osmotic effects. One hundred mM sucrose concentrations inhibited turion buoyancy and germination. Turions formed one primary abscission layer which separated them from the stolon and the mother frond. Subepidermal idioblasts appeared to seal the stolon stump after separation.
FLORAL MORPHOLOGY OF HORSFIELDIA (MYRISTICACEAE)
Authors: Armstrong J. E. , Wilson T. K.
Published: January 2018

The pistillate flowers of Horsfieldia are morphologically similar to those of Myristica and Knema, and are composed of a single whorl of thick, fleshy tepals, and an unsealed, monocarpellate pistil bearing a single ovule. The carpel is vascularized by two ventral bundles, a pair of dorsal bundles, and several supernumerary bundles. The ovule vascularization is derived from the supernumerary bundles. Paired dorsal vascular bundles are an uncommon feature of uncertain significance. Carpels of Myristica and Knema lack any clearly defined dorsal vasculature, and the ovule vascular supply is derived from both the ventral and supernumerary bundles. The organization of the staminate flowers of Horsfieldia agrees with the myristicaceous pattern observed in Myristica and Knema. Each androecium consists of a single whorl of anthers fused or partially fused to a massive connective column. Each anther consists of a pair of bisporangiate lobes and a single vascular bundle. The androecial forms observed are interpreted as forming a series of intermediates between the monadelphous type of androecia of two South American genera, Compsoneura and Dialyanthera, and one African genus, Brochneura, and the solid, columnar androecia which are predominate in the family. Accumulating evidence supports a proposed South American or west Gondwanaland origin of the Myristicaceae.
SPECIAL PAPER: SYSTEMATICS AND EVOLUTION OF SORGHUM SECT. SORGHUM (GRAMINEAE)
Authors: de Wet J. M. J.
Published: January 2018

The genus Sorghum Moench is subdivided into sections Chaeotosorghum, Heterosorghum, Parasorghum, Stiposorghum and Sorghum. Section Sorghum includes two rhizomatous species, S. halepense (L.) Pers. (2n = 40) and S. propinquum (Kunth) Hitchcock (2n = 20), as well as the annual S. bicolor (L.) Moench (2n = 20). Sorghum bicolor is divided into subspecies bicolor to include all domesticated grain sorghums, subspecies drummondii (Steud.) de Wet comb. nov. to include stabilized derivatives of hybridization among grain sorghums and their closest wild relatives and subspecies arundinaceum (Desv.) de Wet et Harlan to include the wild progenitors of grain sorghums. Four ecotypes of subspecies arundinaceum are recognized: race aethiopicum of the arid African Sahel. race virgatum of northeastern Africa, race arundinaceum of the African tropical forest, and race verticilliflorum of the African Savanna. The numerous, usually recognized grain sorghums are divided among five basic races, bicolor, caudatum, durra, guinea and kafir, and ten hybrid races that each combine characteristics of at least two of these basic races. Races of grain sorghum are morphologically distinct, and they maintain their unity of type through spacial and ethnological isolation.
IS THE HERMAPHRODITE FLOWERING PLANT EQUISEXUAL?
Authors: Horovitz Auguste
Published: January 2018

The view that, as individuals or genotypes, outcrossing hermaphrodite flowering plants are necessarily equally effective male and female parents, is challenged. The dissimilar selection pressures to which their male and female gametophytes are subjected make this generality unlikely. The breeding population rather than the individual is seen as the level at which the 1:1 ratio between male and female gametes obtains, and phenomena indicative of this situation are discussed. To stabilize hermaphroditism at the norm of equisexuality, special devices which minimize the divergence between male and female gametophytic selection may be needed. Complementary stamen and pistil characters in interbreeding morphs of heterostylous plants are seen as such devices.
CHROMOSOME NUMBERS IN CHIHUAHUAN DESERT CACTACEAE. TRANS‐PECOS TEXAS
Authors: Weedin James F. , Powell A. Michael
Published: January 2018

Chromosome numbers are presented for 100 collections of Cactaceae from the Trans‐Pecos region of Texas. A total of 65 taxa representing 52 species and 12 genera were counted, including first reports for 45 taxa and new ploidy levels for four taxa. Notable among those listed are counts for Opuntia schottii var. grahamii (n = 11, ca. 22), O. stanlyi (n = 22), O. arenaria (n = 11), O. phaeacantha var. spinosibacca (n = 22), O. lindheimeri var. lindheimeri (n = 11), O. strigil (n = 11), Echinocereus enneacanthus var. cf. dubius (n = ca. 22), E. pectinatus var. neomexicanus (n = 22), and Thelocactus bicolor var. bicolor (n = 22). Endomitosis was found to be present in O. phaeacantha var. spinosibacca, Mammillaria pottsii, and Neolloydia intertexta var. dasyacantha. Meiotic irregularities were noted in some species belonging to the genera Opuntia and Echinocereus. Phytogeographic considerations are inferred from the chromosomal data for O. polyacantha, O. lindheimeri, and O. ficusindica. A base number of x = 11 in Cactaceae is supported.
SPECIAL PAPER: THE PLASTOCHRON INDEX: A REVIEW AFTER TWO DECADES OF USE
Authors: Lamoreaux Robert J. , Chaney William R. , Brown Kenneth M.
Published: January 2018

The plastochron index provides a morphological time scale which has proved more reliable than chronological age in studies relating morphological and physiological development of a whole plant or plant organ. Since its inception in 1957, the index has been utilized in a variety of investigations from leaf ontogeny in cottonwood trees to rhizoid cluster initiation in algae. The plastochron index has been extensively used in studies involving source and sink relationships, leaf anatomy, cell differentiation, and primary vascularization. It has been used in investigations of hormonal regulation of plant growth and in studies of the effects of various environmental factors on developmental processes in crops. This paper reviews some of the literature from 1957 to present concerning the development and use of the plastochron index.
THE ULTRASTRUCTURE OF THE DEVELOPING SOROPHORE OF MARSILEA VESTITA
Authors: Bilderback D. E.
Published: January 2018

In the young sporocarp of Marsilea vestita, the sorophore tissue consists of vacuolate parenchymatous cells. The vacuoles contain electron‐dense bodies which disappear as the cells enlarge. During the differentiation of the sorophore cells, there are three phases of polysaccharide accumulation. During the first phase, speroidal carbohydrate bodies accumulate in vesicles and vacuoles of the peripheral cytoplasm. Globular carbohydrate bodies which are interconnected by strands of polysaccharide appear in the central vacuole during the second phase. The third phase begins with the appearance of strands of polysaccharide radiating out into the central vacuole from the tonoplast. As the sorophore cells mature, the central vacuoles become filled with this fibrous polysaccharide. The cytoplasm ultimately degenerates leaving behind dispersed globular carbohydrate and fibrous polysaccharide. When the mature sporocarp is scarified and placed in water, the hygroscopic polysaccharide in the sorophore cells expands and stretches the cell walls. As a result, the sorophore is transformed into a long column many times its original length.
CHROMOSOME NUMBERS IN THE COMPOSITAE. XIV. LACTUCEAE
Authors: Tomb A. Spencer , Chambers Kenton L. , Kyhos Donald W. , Powell A. Michael , Raven Peter H.
Published: January 2018

Reports of 150 original chromosome counts are recorded, including reports of 22 genera and 57 species and subspecific taxa in tribe Lactuceae. Also included are first reports for 12 specific or subspecific taxa. x = 9 appears to be the ancestral base of the tribe. Chromosome numbers are known for over 85% of the genera of the tribe and the frequency of polyploidy is ca. 23%, which is about one‐half that of the angiosperms.
APERTURE EVOLUTION IN THE GENUS PTYCHOPETALUM BENTH. (OLACACEAE)
Authors: Feuer Sylvia M.
Published: January 2018

The genus Ptychopetulum (Olacaceae), disjunct between South America (2 spp.) and Africa (2 spp. West Africa; I sp. Rhodesia), exhibits predominantly diploporate pollen among the West African species and predominantly triporate pollen among the South American taxa. An analysis of aperture evolution suggests two possible schemes of aperture evolution for the genus. Scheme I avers the independent origin of both triporate and diploporate apertures from a basic brevicolpate condition while scheme II proposes a basic diploporate condition in which the diploporate apertures have migrated to the equator, fused to form brevicolpi and have ultimately become reduced to pores. Pollen evidence in support of both schemes is discussed. The distribution of aperture types within the genus also suggests West Africa as the original site of aperture evolution and South America as the second area of aperture development with types traceable to West African stock.
PRODUCTIVITY AND PRODUCTION EFFICIENCY OF AN UPPER SONORAN DESERT EPHEMERAL COMMUNITY
Authors: Patten Duncan T.
Published: January 2018

During years with good winter rainfall, ephemeral plants can contribute considerably to primary production in the upper Sonoran Desert. This study was designed to compare ephemeral community productivity and production efficiency within the different microhabitats created by trees, shrubs and open spaces in a Sonoran Desert ecosystem. Ephemerals were periodically harvested in the different habitats and dried for biomass and caloric determinations. The caloric data were compared to total solar input into the different microhabitats in order to determine production efficiencies of each stand. Productivity rates were also determined for the total community for the sample period, winters of 1972‐74. Both productivity and production efficiency were highest under the shade of Cercidium. The highest production efficiency occurring in the shaded sites was 5.03% which approaches the theoretical maximum photosynthetic efficiency level. The production efficiency of the entire ephemeral community for the whole growing season was only 0.17% during an optimal year, demonstrating the influence of the environment in the interspaces on productivity and solar conversion in the desert.
SILICON IN THE ROOTS OF HIGHER PLANTS
Authors: Sangster A. G.
Published: January 2018

Silicon (Si) distribution in the roots ofSorghastrum nutans(L.) Nash andSorghum bicolor(L.) Moench. was investigated by means of the electron‐probe microanalyzer and scanning electron microscope. In both species, Si was confined to the inner tangential wall of the tertiary‐phase endodermal cells in the form of nodular silica aggregates of similar morphology and X‐ray intensity. The results are compared to those for six closely related genera, as well as to studies of Si in the roots of species of other tribes of the family Poaceae. The various types of root deposits occurring in the family are described, and their relationships discussed. It is concluded that the type of Si distribution exhibited is determined largely by the phylogenetic status of the genus, rather than by the basic pattern of root anatomy.
FLAVONOIDS OF THE PRIMITIVE FERNS: STROMATOPTERIS, SCHIZAEA, GLEICHENIA, HYMENOPHYLLUM, AND CARDIOMANES
Authors: Wallace James W. , Markham Kenneth R.
Published: January 2018

The flavonoids of the primitive leptosporangiate ferns Stromatopteris moniliformis, Schizaea bifida, Gleichenia cunninghamii, Cardiomanes reniforme, and Hymenophyllum demissum have been identified as 3‐O‐glycosides of the flavonols kaempferol and quercetin. None of the examined ferns produced flavonoids which are also common to the Psilotoceae. The Psilotaceae have previously been shown to produce O‐glycosides of amentoflavone (biflavone) and apigenin (flavone) and traces of C‐glycosylflavones (Wallace and Markham, 1978). These data imply that the primitive leptosporangiate ferns are not closely related to the Psilotaceae. The antiquity of rhamnose as a glycosyl moiety is suggested by its occurrence in both the primitive leptosporangiate ferns and in the Psilotaceae.
HETEROPHYLLY IN POPULUS GRANDIDENTATA (SALICACEAE) WITH EMPHASIS ON RESIN GLANDS AND EXTRAFLORAL NECTARIES
Authors: Curtis John D. , Lersten Nels R.
Published: January 2018

Big‐tooth aspen displays heterophylly on twigs of saplings and on upper, vigorously growing twigs of larger trees. Early leaves, those present in overwintering buds which expand in spring, differ from late leaves, those that are mostly initiated and developed during the late spring and summer of the same year. The two sets of leaves differ in size, shape, number of teeth, number of marginal resin glands, and number and size of basilaminar extrafloral nectaries. Secretory structures are generally more prominent and active on late leaves. Marginal resin glands, resin‐secreting stipules, and basilaminar nectaries of both early and late leaves are similar anatomically, having a secretory epidermis of cytoplasmically dense palisade‐like cells separated from vascular bundle endings by several layers of isodiametric parenchyma. These secretory structures, and the dense mat of trichomes which cover the leaf until it fully expands, may help to protect the young leaves from insect damage. The basilaminar nectaries seem especially effective because they attract ants that probably discourage visits by other insects.
COPROMYXELLA: A NEW GENUS OF ACRASIDAE
Authors: Raper Kenneth B. , Worley Ann C. , Kurzynski Terrence A.
Published: January 2018

A new genus of cellular slime molds, Copromyxella, is described together with four species that comprise it. Since it resembles Zopf's Copromyxa more than any genus presently recognized, but differs from it in important characteristics such as the smaller dimensions of its cellular elements and the delicacy of its fructifications, the name Copromyxella is chosen for the new taxon. Four species are included: C. silvatica, C. filamentosa, C. spicata, and C. coralloides. All are characterized by small myxamoebae with lobose and potentially “explosive” pseudopodia and may assume limax forms in liquid media; all possess nuclei with centrally positioned nucleoli; all lack true contractile vacuoles (with a single possible exception); all aggregate without stream formation; and all form fructifications with no demarcation into stalks and sori. Taxonomically the genus belongs in the Acrasidae with Copromyxa, Guttulinopsis and Acrasis rosea rather than in the better known Dictyostelidae that includes Dictyostelium and Polysphondylium.
CARBOHYDRATE MOBILIZATION AND MOVEMENT IN ALPINE PLANTS
Authors: Wallace Linda L. , Harrison A. Tyrone
Published: January 2018

Starch retention and disappearance from leaves and carbon movement under various temperatures were studied in two alpine species, Oxyria digyna (L.) Hill and Phleum alpinum L., and in two low‐elevation species, Helianthus annuus L. and Elymus canadensis L. The alpine species exhibited starch disappearance from the leaf following cool night temperatures, whereas starch retention was noted under similar conditions for the low‐elevation species. The alpine species, Oxyria, exhibited the highest rates of starch disappearance from the leaf under cool temperatures as well as the highest carbohydrate translocation under cool temperatures. The low‐elevation species had low rates of starch disappearance and carbohydrate translocation under low temperatures, but exhibited relatively higher rates with an increase in temperature. Such a mechanism whereby alpine species can maintain relatively high rates of translocation under cold temperature represents a major form of physiological adaptation to the short, cool, growing season in the alpine tundra.
FEATURES OF POLLEN FLOW IN DIMORPHIC SPECIES OF LYTHRUM SECTION EUHYSSOPIFOLIA
Authors: Ornduff Robert
Published: January 2018

The North American Lythrum lineare L., L. alatum Pursh, L. curtissii Fernald, and L. californicum T. & G. have distylous flowers that differ in a number of traits. In the two species examined, pins have a stronger incompatibility system than thrums. Pins outnumber thrums in natural populations, but the ratio of the two may change radically during the course of a year, probably as a result of sexual reproduction. Exotic honeybees visiting L. californicum exhibited preferential collection of pin pollen over thrum pollen. The relative proportion of pin and thrum pollen grains transferred to stigmas is not dependent upon the proportion in which these pollen grains are produced in a population. Analyses of stigmatic pollen loads of L. lineare and L. californicum indicate very high levels of intramorph pollen flow. Although distyly is likely derived from tristyly in Lythrum, pollen flow patterns in trimorphic species seem to operate more “efficiently” than in dimorphic ones. It is probable that distyly has evolved from tristyly several times in the Lythraceae, but comparisons between pollen flow patterns in distylous species and those in a tristylous species provide no clear insights into the selective pressures that have led to this fundamental change in floral morphology and reproductive system.
THE ULTRASTRUCTURE OF PHYCOPELTIS (CHROOLEPIDACEAE: CHLOROPHYTA). I. SPOROPOLLENIN IN THE CELL WALLS
Authors: Good Barry H. , Chapman Russell L.
Published: January 2018

Electron microscope observations onPhycopeltis epiphyton, a subaerial green alga found growing on the leaves of vascular plants and bryophytes, revealed the presence of a densely staining material within the inner and outer zones of the cell walls. This material resists acetolysis, is degraded by chromic acid, is unaffected by ethanolamine and exhibits secondary fluorescence when stained with the fluorochrome Primuline. These characteristics, together with infrared absorption spectra indicate that, on the basis of currently accepted criteria, the densely staining material is a sporopollenin and that it is a major component of the cell wall. Tests for cellulose, chitin, and lignin were negative, and little if any silica is present. It is suggested that negative results in tests for cellulose may be due to a masking effect by the sporopollenin. Comparison of the fine structure of the cell walls ofP. epiphyton, pollen grains, and algal cells (known to contain sporopollenin) supports the suggestion that sporopollenin deposition on “unit membranes” is universal. Morphological similarity among sporopollenin lamellae inP. epiphyton, pollen grains, spores of land plants, and the trilaminar sporopollenin sheath inChlorella, Scenedesmus, andPediastrumindicates that the structures may be analogous. As in pollen grains, sporopollenin may provide protection against desiccation and parasitism. It may also be involved in the adhesion ofPhycopeltisto host plants and in the adhesion between adjacent filaments of the thallus.