bluuebunny/crossref_metadata_2025 huggingface dataset:
POLLEN INTERFERENCE AND CRYPTIC SELF‐FERTILITY IN CAMPSIS RADICANS
Authors: Bertin Robert I. , Sullivan Maura
Published: January 2018

The effect of self pollen on the success of cross pollinations was studied in Campsis radicans (L.) Seem., a species previously considered self‐sterile. The application of self pollen to stigmas in combination with or preceding the application of cross pollen markedly reduced the likelihood of fruit production. This effect was not due to the dilution of cross pollen nor to physical blocking of the stigmatic surface, since mixtures of talc and cross pollen were as effective as pure cross pollen in causing fruit production. Pollen tubes produced by self pollen grew at rates similar to those from cross pollen, and penetrated the ovary. The interference caused by self pollen appears to take place in the ovary, although it cannot be stated to what degree it is prezygotic or postzygotic. The marked protandry occurring in C. radicans is presumed to be due at least partly to selection for avoidance of these negative effects on female reproductive success. Up to 33% of viable seeds from mixed self + cross pollinations were sired by self pollen. The term “cryptic self‐fertility” is coined to describe this phenomenon where pollination with loads of pure self pollen rarely or never yields fruit, but pollination using mixtures of self and cross pollen yields fruit containing considerable numbers of selfed seed. Estimates of selfing frequency that are based on pollination using loads of purely self pollen will be in error for species possessing cryptic self‐fertility.
COLONIZING PLANTS ON THE PUMICE PLAINS, MOUNT ST. HELENS, WASHINGTON
Authors: Wood David M. , Moral Roger del
Published: January 2018

Initial colonization on the devastated Pumice Plains on the northern flank of Mount St. Helens, Washington, was monitored in two large grids seven seasons after the eruptions of 1980. The Pumice Plains is composed primarily of deep pumice, but contains a few large mudflow channels and numerous small erosion gullies. Over 45% of 1,600 10 by 10 m quadrats (Willow Spring site) and over 35% of 875 quadrats (Lupine Patch site) were devoid of vascular plants. The most common species were the weedy natives, Anaphalis margaritacea and Epilobium angustifolium, as well as Lupinus lepidus var. lobbii, a native with poor dispersal usually found at subalpine elevations. The first two species invaded by long‐distance dispersal; a few individuals of the latter somehow established by 1981 from surviving rootstocks or seeds, and dense populations have developed from these survivors. Other species are typically found at low densities in favorable microsites. Species richness averaged 1.03 per 100 m2 at Willow Spring and 1.82 at Lupine Patch. There are 32 species at Willow Spring and 26 at Lupine Patch. Species richness was concentrated in sites with high soil moisture and where topographic irregularities permitted accumulation of seeds. Colonists are an unusual mix of natives, drawn from an array of open habitats, and introduced weeds originating in fields and clearcuts at lower elevations. Colonizing species are primarily herbaceous, perennial, and wind‐dispersed, though seedlings of woody “climax” species occur. Three distributional patterns are recognized: hydrophiles, found near streams; facultative hydrophiles, concentrated in wet sites but successfully colonizing upland sites; and species distributed at random or in xeric sites. We predict that the course of succession will continue to be slow and herbs‐dominated. Patches of Lupinus lepidus at present do not appear to facilitate colonization. Colonists will continue to be rare and be confined to favorable microsites for several years.
NATURAL INTERSPECIFIC HYBRIDIZATION IN EASTERN NORTH AMERICAN CLAYTONIA
Authors: Doyle Jeff J. , Doyle Jane L.
Published: January 2018

The eastern North American spring ephemeral Claytonia virginica (Portulacaceae) is well known for its great variation in chromosome number. The origin and significance of this cytological diversity has been a source of some controversy over the last two decades; in particular it has been suggested that one major source of variation could have arisen by allopolyploidy following hybridization between C. virginica and the second eastern North American representative of the genus, C. caroliniana. However, there has been no rigorous demonstration of natural hybridization between these taxa, and attempts to document hybridity have been hampered by a paucity of distinguishing morphological characters. Nuclear ribosomal gene markers are, however, able to distinguish between the two species and provide a means of identifying hybrid plants. We have found a locality in central New York state where the two species cooccur; in this population, hybrid individuals with additive ribosomal gene patterns are found in a zone of overlap between the two parental species. These hybrids are morphologically intermediate and have reduced pollen stainabilities, and appear to be F1 individuals.
RAPID SCREENING METHOD TO DETECT POTENTIAL BIPARENTAL INHERITANCE OF PLASTID DNA AND RESULTS FOR OVER 200 ANGIOSPERM SPECIES
Authors: Corriveau Joseph L. , Coleman Annette W.
Published: January 2018

We have developed a diagnostic method to screen rapidly for plant species potentially capable of biparental inheritance of plastid DNA using the DNA fluorochrome 4′,6‐diamidino‐2‐phenylindole (DAPI) in conjunction with epifluorescence microscopy. Pollen shed from 235 plant species (including about 50 of agronomic importance) representing 80 families were screened. Putative plastid DNA was detected in the generative and/or sperm cells of pollen from 26 genera (43 species) representing 15 families. Plastid DNA was not detected in the generative or sperm cells of pollen from 192 plant species, thereby strongly suggesting that these species have only maternal inheritance. Our cytological diagnosis corroborated the known genetic evidence in 42 plant species and conflicted with the genetic reports in five species, which are discussed. The data suggest that biparental inheritance of plastids is rare; overall, it may occur in about 14% of flowering plant genera, examples of which are scattered among 19% of the families examined. This methodology also readily reveals whether pollen is bi‐ or trinucleate.
TRIASSIC FUNGUS FROM ANTARCTICA WITH POSSIBLE ASCOMYCETOUS AFFINITIES
Authors: White James F. , Taylor Thomas N.
Published: January 2018

Hyphae, sporocarps, and structures which appear to represent arthroconidia are described from silicified peat deposits of Triassic age from Antarctica. Sporocarps with a single ostiole possess a multilayered wall with internally produced aseptate appendages that ornament the sporocarp surface. The primitive features exhibited by this fungus, together with previously described sporocarps, provide evidence for the existence of a group of fungi that may be ancestral to modern Ascomycotina.
INFLUENCE OF AGE AND MICROCLIMATE ON THE PHOTOCHEMISTRY OF RHODODENDRON MAXIMUM LEAVES II. CHLOROPLAST STRUCTURE AND PHOTOSYNTHETIC LIGHT RESPONSE
Authors: Nilsen E. T. , Stetler D. A. , Gassman C. A.
Published: January 2018

The influence of age on chloroplast structure and photosynthetic light response of Rhododendron maximum L. was studied in three different microhabitats. The three microhabitats constituted a gradient of low, intermediate, and high irradiance levels. The most dramatic change in chloroplast structure with increasing age was the proliferation of the number and size of plastoglobuli. The magnitude and age specific rate of chloroplast occlusion by plastoglobuli increased in habitats with higher irradiance. Photosynthetic responses to light differed among the age categories of leaves. Light saturated photosynthesis and quantum yield decreased as leaves aged. However, in high light environments the rate of reduction of quantum yield or light saturated photosynthetic rate was more rapid than in the low light environment. The quantity of plastoglobuli increased in association with reduced light reaction capacity. The presence and abundance of plastoglobuli in R. maximum chloroplasts and their association with reduced photosynthetic performance indicates that the photosynthetic apparatus of the R. maximum chloroplast is sensitive to photodestruction by high irradiance: commonly a winter phenomenon in these environments.
DISTRIBUTION AND RELATIONSHIP OF CELL DIVISION AND MATURATION EVENTS IN PISUM SATIVUM (FABACEAE) SEEDLING ROOTS
Authors: Rost Thomas L. , Jones Todd J. , Falk Richard H.
Published: January 2018

Pea roots have open apical organization, where discrete initial cells do not exist. Differentiation of all tissues occurs in cylinders and vascular sectors that blend gradually with each other. This study reports the distribution of dividing cells and their relationship to maturation events in the 2 mm root tip, and in the 8–10 and 18–20 mm segments. Up to 200 μm from the root body/cap junction, cell division is uniformly distributed throughout all meristem regions. By 350 to 500 μ, xylem tracheary elements and cells of the pith parenchyma and middle cortex have stopped dividing. At this level cell division is almost entirely restricted to two cylinders, one composed of the inner root cap, the epidermis, and the outer cortex (outer cortex cylinder) and another composed of cells of the inner cortex, the pericycle and vascular tissue (inner cortex cylinder). When the protophloem matures, all cells in the phloem sector of the inner cortex cylinder, including the 1 layered pericycle, the endodermis and the phloem parenchyma, stop dividing. The 3–4 layered pericycle in the xylem sectors continues dividing until about 10 mm from the body/cap junction following the maturation of the protoxylem tracheary elements.
EFFECTS OF SHOOT INVERSION ON STEM STRUCTURE IN PHARBITIS NIL
Authors: Prasad Tottempudi K. , Sack Fred D. , Cline Morris G.
Published: January 2018

The effects of shoot inversion on stem structure over 72 hr were investigated in Pharbitis nil by analyzing cell number, cell length, and the cross sectional areas of cells, tissues, and regions. An increase in stem diameter can be attributed to an increase in both cell number and cross sectional area of pith (primarily) and vascular tissue (secondarily). Qualitative observations of cell well thickness in the light microscope did not reveal any significant effects of shoot inversion on this parameter. The inhibition of shoot elongation was accompanied by a significant decrease in cell length in the pith. The results are generally consistent with an ethylene effect on cell dimensions, especially in the pith.
EFFECTS OF HYBRIDIZATION AND INBREEDING ON FITNESS IN PHLOX
Authors: Levin Donald A. , Bulinska‐Radomska Zophia
Published: January 2018

The effects of interpopulation hybridization, and self‐fertilization and immigration on fitness in Phlox drummondii were analyzed in 5 natural field sites. Germination rates, survivorship to flowering, fecundity, and net reproductive rates (Ro) were determined for planted populations of natives, hybrids, aliens, and the products of one and two generations of self‐fertilization.

At all sites, seed germination was 36% for natives, 35% for hybrids and 28% for aliens. Survivorship for natives was 50%, compared to 49% for hybrids and 41% for aliens. The mean fecundity was 34, 35, and 39 seeds per plant for natives, hybrids, and aliens, respectively. The Ro of natives averaged 5.2 vs. 6.4 for hybrids and 4.2 aliens. At all the sites, germination averaged 25% for self‐1 plants and 19% for self‐2 plants compared to 24% for open‐pollinated controls. Survivorship progressed from 50% in the controls to 46% in self‐1 and 44% in self‐2 plants. Seed production per plant averaged 35% in the control vs. 32% in the self‐1 and 25% in the self‐2 plants. The mean Ro of the control was 3.8 vs. 3.3 in the self‐1 and 2.14 in the self‐2 plants. Our results demonstrate that the genetic variable may have a substantial effect on plant fitness in the field.
DIOECISM AND ITS CORRELATES IN THE CAPE FLORA OF SOUTH AFRICA
Authors: Steiner Kim E.
Published: January 2018

Floral sexuality is characterized for the flora of the Cape region of South Africa. Among angiosperms (N = 8,497), monostylous hermaphroditism constitutes the largest proportion of species with 77.7%, followed by gynomonoecism (7.1%), dioecism (6.6%), andromonoecism (4.0%), monoecism (2.6%), heterostylous hermaphroditism (1.9%), polygamomonoecism (0.01%) and polygamodioecism (0.01%).

The incidence of dioecism is significantly higher (P < 0.001) at the species level for two smaller floras within the Cape flora that consist mostly of species‐rich fynbos vegetation (Cape of Good Hope Nature Reserve: 11.6% [N = 1,349], Cape Hangklip: 9.7% [N = 1,046]). The relatively high incidence of dioecism in all three floras compared to other temperate floras is due to the large number of Restionaceae species. Excluding these rush‐like plants, dioecism at the species level is only 3.0% for the Cape flora, 4.2% for the Cape Hangklip flora and 3.6% for the Cape of Good Hope flora. At the generic level there are no significant differences in the incidence of dioecism between the three floras.

Among dioecious species and genera in the Cape flora, there is a higher than expected incidence of wind pollination, fleshy fruits and nonwoodiness when each variable is analyzed independently. The association between nonwoodiness and dioecy has not been reported for other floras and is due to the large proportion of nonwoody wind‐pollinated Restionaceae. If this family is excluded from the analysis, dioecy becomes associated with biotic pollination, fleshy fruits, and woodiness.

Interactions among the variables themselves as well as with dioecism indicate the need for a joint analysis of the variables. At the genus level, analyses reveal the following: 1) There is a higher than expected incidence of wind pollination among dioecious plants with dry fruits. If the Restionaceae are excluded from the analysis, wind pollination is more common than expected only for woody plants with dry fruits. 2) Dioecious plants that are biotically pollinated have a significantly higher incidence of fleshy fruits than expected. 3) Dioecious plants with dry fruits that are biotically pollinated have a higher than expected incidence of woodiness. If the Restionaceae are excluded from the analysis, woodiness is more common than expected among both nonwind and wind‐pollinated dioecious genera.
EFFECTS OF ELEVATED CARBON DIOXIDE ON ESTIMATION OF LEAF AREA AND LEAF DRY WEIGHT OF SOYBEAN
Authors: Leadley Paul W. , Reynolds James F.
Published: January 2018

The objectives of this study were to determine the effects of elevated CO2 on relationships between leaf area (A) and linear leaf dimensions (length [L] and width [W]) and leaf dry weight (M) in soybeans (Glycine max (L.) Merr. cv. Bragg). Based on dimensional measurements made on trifoliolates 1–6 for plants grown under three CO2 levels (348, 502 and 645 μl l−‐1), the best predictor for both trifoliolate leaf area and for fully expanded central leaflets of the trifoliolates was an equation of the form A = bo + b1L·W; these relationships were unaffected by CO2, although there was a small effect of leaf position. For expanding central leaflets of the fifth trifoliolate, no CO2, leaf size (age) or CO2 × leaf size effect was found. Specific leaf weight (i.e., M/A) was significantly affected by CO2, increasing with increasing CO2. Hence, trifoliolate dry weight can be nondestructively estimated from trifoliolate area using the equation M = 0.097 + (6.71 × 10−‐3 + 1.04 × 10−‐6[CO2])A, where [CO2] is mean daytime CO2 concentration of the growth environment.
BREEDING SYSTEM IN FICUS CARICA, THE COMMON FIG. I. FLORAL DIVERSITY
Authors: Beck N. G. , Lord E. M.
Published: January 2018

Coevolution in Ficus carica (Moraceae) and the fig wasp (Blastophaga psenes, Agaonidae, Chalcidoidea) has resulted in a complex breeding system involving two tree morphs (Caprifig and Edible fig), three floral forms (long‐styled female, short‐styled female, and male flowers) and the insect pollinator. The two female floral forms have been reported to differ only in style length and stigma shape. In the present study, we demonstrate that the two female flowers differ from inception—short‐styled flower primordia are smaller and exhibit significantly greater individual variation than do those of the long‐styled flower, and the relative growth rate of each flower type differs. Mature forms exhibit disparity in style length, in stigma characteristics, and in degree of fusion of stylar lobes. Female flowers of both tree morphs are unisexual from inception. Male flowers of the Caprifig tree morph are initiated as hermaphrodites and gynoecium abortion occurs before megaspore mother cell stage. A single inflorescence therefore expresses two pathways to unisexuality. Hermaphrodite flower primordia were repeatedly found in the supposedly unisexual female syconium of the Edible fig tree morph. Based on its developmental morphology, Ficus carica appears to be of gynomonoecious ancestry.
BREEDING SYSTEM IN FICUS CARICA, THE COMMON FIG. II. POLLINATION EVENTS
Authors: Beck N. G. , Lord E. M.
Published: January 2018

Pollination events are examined in Ficus carica, the common fig. The stigma of the long‐styled female flower is wet. Stigma and stylar secretions consist of mucopolysaccharides, lipids, and insoluble carbohydrates. The pollen from anthers of the male flowers is dimorphic, being tri‐ and diporate. Pollen tubes grow in intercellular secretions of the solid style until they reach the obturator which forms on the funiculus of the ovarian cavity. The obturator secretes primarily insoluble carbohydrates which remain sequestered under the cuticle. A pollen tube grows through the stylar tissues emerging beneath the cuticle of the obturator into these secretions and then penetrates the micropyle. Differences were observed between timed pollination trials in two sites in California. At one site, a characteristic coiling of pollen tubes occurred in the region of the funiculus before pollen tube penetration of the micropyle. At the other site, presyngamy pollen tube coiling was not observed and pollen tube growth rates were doubled. There were higher temperatures at the second site during the pollination experiment. The stigma of the short‐styled flowers is nearly dry, and the transmitting tract shows decreased amounts of secretion. The funiculus did not have a differentiated obturator and secretions there were insufficient to raise the cuticle over the micropyle. The short‐styled flowers appear to be losing their ability to function as fully viable females.
DEVELOPMENTAL ANATOMY OF THE HORNED OAK GALL INDUCED BY CALLIRHYTIS CORNIGERA ON QUERCUS PALUSTRIS (PIN OAK)
Authors: Taft John B. , Bissing Donald R.
Published: January 2018

The horned oak gall forms on twigs of Quercus palustris Muench. and is initiated when the wasp Callirhytis corrigera O.S. oviposits into the periderm or cortex of the twigs. Injury to phellogen as a consequence of oviposition results in dedifferentiation of phelloderm and underlying phloem tissue to form a wound‐response phellogen. The wound‐response phellogen encircles and compartmentalizes the wasp ovum and is continuous with the normal stem phellogen. This tissue arrangement forms the framework for the ensuing stages of gall development. Development of the insect larva coincides with the formation of a gall‐matrix phellogen. This additional meristem is derived from locally hyperplastic stem phellogen where adjacent to the wound‐response phellogen. The essentially parenchymatous, roughly spherical body of the gall, the gall matrix, is formed chiefly from derivatives of the gall‐matrix and wound‐response phellogens. In the immediate area of the wasp larva, the wound‐response phellogen produces cells toward the larva that differentiate to form a vascularized, externally sclerified, horn‐shaped chamber containing in its base the developing insect larva. The involvement of the vascular cambium is apparent during intermediate gall development stages. Vascular strands, produced transverse to the stem axis, penetrate the gall‐matrix tissue and terminate near the base of the horn‐like larval chamber. Vessel elements in the region of the gall that are not included in this tissue alteration often become heavily tylosed. Disruption of the vascular tissue through the galled area appears to be a primary cause of twig death.
FLOWER DEVELOPMENT IN NORMAL TOMATO AND A GIBBERELLIN‐DEFICIENT (ga‐2) MUTANT
Authors: Nester Joan E. , Zeevaart Jan A. D.
Published: January 2018

Flower buds of a tomato (Lycopersicon esculentum Mill.) gibberellin‐deficient mutant (ga‐2/ga‐2) were initiated, but did not develop to maturity and eventually aborted. If GA, was applied to a developing inflorescence or stem tip, completion of flower bud development and fruit set occurred. In development of the ga‐2 flowers, the corolla and stamens did not elongate and the style was misshapen or extended past the tip of the anthers. Light microscope observations indicated that meiosis of both microsporocytes and megasporocytes did not occur. Cells of the sporogenous layer were initiated, but growth was arrested and they eventually degenerated. The ovary was normal in appearance. However, the megasporocytes degenerated, giving rise to a cavity in the ovule. Thus, although GA is not required for flower initiation in tomato, it is essential for meiosis of the microsporocytes and megasporocytes and elongation of the corolla and stamens.
GENETIC VARIATION AND DIFFERENTIATION IN THE GENUS MABRYA (SCROPHULARIACEAE‐ANTIRRHINEAE): SYSTEMATIC AND EVOLUTIONARY INFERENCES
Authors: Elisens Wayne J. , Crawford Daniel J.
Published: January 2018

Nine populations of the five species of Mabrya have been examined for allozyme variation at 22 loci using enzyme electrophoresis. The species are homoploid (n = 12), herbaceous perennials and occur in small populations in canyons and barrancas in North American desert scrub and thorn scrub habitats. Although of ancient polyploid origin, the number of isozymes considered typical for diploids is encountered except for a probable duplication at a TPI locus. The average interspecific pairwise comparisons of genetic identities (range 0.434–0.731) are very dissimilar to intraspecific values (range 0.886–0.968). The uniformly low interspecific genetic divergence estimates (average I value of 0.593), large number of unique alleles (average of five per species), pronounced morphological differences, reduced interspecific cross‐compatibilities, and (usually) allopatric distributions support recently proposed specific and infrageneric delimitations and hypotheses of a geographical speciation mode, a long period of reproductive isolation, and relictual endemism. Estimates of populational genetic variation are concordant with previous reproductive observations and suggest an outcrossing breeding system for M. geniculata and a mixed mating system for the other species. Because of approximately similar divergence values, phylogenetic relationships in the genus remain unresolved.
MEGAGAMETOPHYTE ORGANIZATION IN A POLYEMBRYONIC LINE OF LINUM USITATISSIMUM
Authors: Secor Diana Lenard , Russell Scott D.
Published: January 2018

A haploid‐diploid twin‐producing polyembryonic line “RA91” of Linum usitatissimum L., flax, known to produce twin embryos with a frequency in excess of 32% was employed to determine the cytological factors relating to the production of haploid embryos using light and transmission electron microscopy. Potentially polyembryonic flax megagametophytes contain at maturity either a conventional 3‐celled egg apparatus (36% of megagametophytes), or contain supernumerary eggs forming either a 4‐ (50%) or 5‐celled (14%) egg apparatus. In megagametophytes with supernumerary eggs, one egg cell appears to occupy the conventional position, whereas additional supernumerary eggs surmount the synergids and are smaller cells presumably derived from division of the true egg. Although supernumerary eggs appear similar in ultrastructure, they differ in location, size, and unlike typical egg cells, appear to have a complete, contiguous cell wall adjacent to the synergid. Such supernumerary cells are postulated as the origin of such haploid embryos, with the diploid member formed by conventional fertilization events with the micropylar egg.
MALE STERILITY IN SOYBEAN‐AN OVERVIEW
Authors: Graybosch Robert A. , Palmer Reid G.
Published: January 2018

The most common type of reproductive mutations observed in the soybean [Glycine max (L.) Merr.] are those that induce male sterility. The high frequency of occurrence of male‐sterile mutations indicates that a number of genes influence the processes of microgametogenesis and microsporogenesis. The current knowledge of these mutations is summarized. The origins of male‐sterile mutations, their inheritance patterns, and known linkage relationships are detailed. The phenotypic expression of male‐sterile mutations, including their effects on both male and female reproduction, is discussed. The influence of environment on the expressivity of male‐sterile mutations, and the effects of male‐sterile mutations on physiological processes (senescence and nitrogen fixation) are summarized. Male‐sterile mutations have been useful in the study of soybean reproduction, genetic and cytogenetic investigations, and in evaluating the potential for commercial production of hybrid soybeans. These various applications of male‐sterile mutations are presented.
HETEROMORPHIC FLOWER DEVELOPMENT IN NEPTUNIA PUBESCENS, A MIMOSOID LEGUME
Authors: Tucker Shirley C.
Published: January 2018

The characteristic of heteromorphic inflorescences in some mimosoid legumes such as Neptunia is a puzzling one which can be approached developmentally. Each spicate inflorescence of Neptunia pubescens includes three types of flowers: perfect in the upper half, functionally male just below the middle, and sterile or neuter at the base. Developmental studies of the inflorescence show that order of initiation of bracts on the inflorescence is acropetal, but that order of subsequent development of flowers is both acropetal and basipetal on the axis. Bract growth and initiation of the axillary floral apices at the base are inhibited or retarded, while those in the middle and upper levels continue development without interruption. The three types of floral primordia are similar during initiatory stages of organ formation and through early development. At mid‐development, differences arise in floral symmetry, petal form, stamen form, and size and shape of the carpel. The functionally male flowers become strongly dorsiventral and zygomorphic while the other two morphs remain actinomorphic or nearly so. Heteromorphy arises from a combination of early suppression of organogeny plus mid‐stage innovations of zygomorphy and lateral expansion of stamen primordia. These divergent developmental pathways in one inflorescence can be interpreted in part using Gould's concept of heterochrony: changes in timing of developmental events to produce different structures. Other changes in Neptunia cannot be explained by this concept, however; such changes as omission of processes (i.e., meiosis) in some organs, or addition of processes not normally present (i.e., blade formation in stamen primordia which become staminodia). It is becoming evident from work on this and other legume flowers that actual loss of organs is rare, compared to initiation followed by suppression or modification.
ARE LYCOPODS WITH HIGH CHROMOSOME NUMBERS ANCIENT POLYPLOIDS?
Authors: Soltis Douglas E. , Soltis Pamela S.
Published: January 2018

It has been established that the number of isozymes (different forms of an enzyme encoded by different gene loci) is highly conserved in diploid angiosperms and gymnosperms. In contrast, allopolyploid angiosperms display an increase in isozyme number due to the addition of divergent genomes. Lycopods (Microphyllophyta) are an ancient lineage of vascular plants having very high chromosome numbers. It has been maintained that lycopods acquired these high chromosome numbers through repeated episodes of polyploidy. Despite high chromosome numbers, however, lycopod species having the lowest chromosome numbers within genera possess the number of isozymes typical of diploid seed plants for all enzymes examined except triosephosphate isomerase. There is, therefore, no genetic evidence from enzyme electrophoresis for polyploidy in these plants. These results are comparable to findings for other homosporous pteridophytes including the ferns (Pteridophyta) and horsetails (Arthrophyta). Alternative hypotheses for widespread genetic diploidy in homosporous pteridophytes are 1) repeated cycles of allopolyploidy followed by gene silencing; 2) repeated cycles of autopolyploidy, which would result in duplicated, but not divergent genes for isozymes; 3) initiation of these lineages with relatively high chromosome numbers.
TRANSLOCATION IN POLYTRICHUM COMMUNE (BRYOPHYTA) I. CONDUCTION AND ALLOCATION OF PHOTOASSIMILATES
Authors: Thomas Robert J. , Schiele Edwin M. , Scheirer Daniel C.
Published: January 2018

Leafy stems and connecting underground rhizomes ofPolytrichum communeHedw. contain leptome tissues similar in structure to phloem. Isolated stems in clonal groupings were pulse labelled with14CO2. Labelled sugar, mostly sucrose, glucose, and fructose, appeared in the pulse labelled stems 30 min after treatment. A small amount (3.3%) of labelled sugar was transported to neighboring stems. Silver grain deposition in microautoradiographs of interconnecting rhizomes occurred predominantly over leptome tissues. Increased amounts of translocated radioactivity appeared in starch and cell wall polysaccharide pools one week and six weeks after treatment. These results 1] indicate that transport of photoassimilate occurs through the leptome of perennating rhizomes, 2] demonstrate that translocated carbon is subsequently utilized or stored, and 3] raise important questions about the significance of long distance transport in the life strategy of this complex clonal moss.
PRICKLE DISTRIBUTION IN ARALIA SPINOSA (ARALIACEAE)
Authors: White Peter S.
Published: January 2018

The density of Aralia spinosa prickles varied with the age and architectural position of annual increments. Prickles were most common on young (1–4 years old, 2–3 m tall), unbranched stems. Prickles were less common on branches and were absent on inflorescences. Ramets that grew as sprouts after injury had more and longer prickles than ramets that had not arisen in this way. Leaf prickles were also more common on the leaves of trunk annual increments than on the leaves of branch annual increments. As with stem prickles, leaf prickles were more common on the leaves of stems that had sprouted after cutting than on the leaves of ramets that had not been previously cut. As bark developed, stem prickles were lost at a rate of about 10% per year. While dense prickles characterized young individuals, older individuals (>15 years old) had very few prickles.
MORPHOLOGY AND VASCULATURE OF THE LEAF OF POTATO (SOLANUM TUBEROSUM)
Authors: McCauley M. Michele , Evert Ray F.
Published: January 2018

The leaf and stem of the potato plant (Solanum tuberosum L. cv. Russet Burbank) were studied by light microscopy to determine their morphology and vasculature; scanning electron microscopy provided supplemental information on the leaf's morphology. The morphology of the basal leaves of the potato shoot is quite variable, ranging from simple to pinnately compound. The upper leaves of the shoot are more uniform, being odd pinnate with three major pairs of lateral leaflets and a number of folioles. The primary vascular system of the stem is comprised of six bundles, three large and three small ones. The three large bundles form a highly interconnected system through a repeated series of branchings and arch‐producing mergers. Two of the three large bundles give rise to short, lateral leaf traces at each node. Each of the small bundles in the stem is actually a median leaf trace which extends three internodes before diverging into a leaf. The three leaf traces enter the petiole through a single gap; thus the nodel anatomy is three‐trace unilacunar. Upon entering the petiole, each of the laterals splits into an upper and a lower lateral. Whereas the upper laterals diverge entirely into the first pair of leaflets, the lower laterals feed all of the lateral leaflets through a series of bifurcations. Prior to their entering the terminal leaflet, the lower laterals converge on the median bundle to form a single vascular crescent which progresses acropetally into the terminal leaflet as the midvein, or primary vein. In the midrib, portions of the midvein diverge outward and continue as secondaries to the margin on either side of the lamina. Near the tip of the terminal leaflet, the midvein consists of a single vascular bundle which is a continuation of the median bundle. Six to seven orders of veins occur in the terminal leaflet.
PINUS × CRITCHFIELDII, A LATE PLEISTOCENE HYBRID PINE FROM COASTAL SOUTHERN CALIFORNIA
Authors: Axelrod Daniel I. , Hill Thomas G.
Published: January 2018

Fossil cones buried in an old landslide at San Clemente are dated at 30,000–34,000 BP (years before present). They generally resemble cones of the natural hybrid Pinus radiata × P. attenuata at Año Nuevo, and also the artificial hybrid P. × attenuradiata. But differences in cone shape, size, and apophyses suggest that the fossil P. × critchfieldii Axelrod and T. G. Hill represents a hybrid of populations of P. radiata and P. attenuata then in coastal southern California. This agrees with population differences between these species in central and southern California during the Pleistocene. Regional comparisons of Late Pleistocene floras indicate that at San Clemente mean annual rainfall was about 580–635 mm, or twice that of today, mean annual temperature was about 2.5 C cooler (13.5 vs. 16.0 C), the mean monthly range was lower (5.9 vs. 7.7 C), the growing season was about 40 days shorter (170 vs. 210 days), and equability was higher (M 72 vs. M 67). Forest was replaced by coastal sage scrub and grassland along the San Clemente coast as drier, warmer climate developed after 12,000 BP.
STABILITY OF LEAF VARIEGATION IN SAINTPAULIA IONANTHA DURING IN VITRO PROPAGATION AND DURING CHIMERAL SEPARATION OF A PINWHEEL FLOWERING FORM
Authors: Peary James S. , Lineberger R. Daniel , Malinich Timothy J. , Wertz Monica K.
Published: January 2018

Plants of the foliarly variegated cultivar Saintpaulia ionantha Tommie Lou and the florally variegated cultivar Candy Lou were regenerated through tissue culture from leaf sections, petal sections, and subepidermal tissue. This provided explants with derivatives of all histogen layers of the shoot apex, layers I and II only, and layers II and III only. Over 1,000 plants of Tommie Lou and Candy Lou were grown to flowering. A low level of phenotypic variation was observed, but in no case could this be attributed to the separation of genotypically distinct cell lines. The foliar variegation pattern of both cultivars was stable through in vitro propagation. In contrast, the chimeral components of the flower color pattern in Candy Lou separated during regeneration. These data demonstrate that Tommie Lou‐type foliar variegation is not caused by periclinal chimerism and that all leaf cell layers possess the genetic information necessary to produce variegated foliage. The production of all green and all white plants from a radiation‐induced periclinal chimera demonstrated that the system used could detect chimeral separation. These results support the contention that adventitious shoots in Saintpaulia almost always differentiate in vitro from a derivative(s) of a single histogen layer, and this layer is usually the LI.
POLLEN WALL ULTRASTRUCTURE OF SELECTED DISPERSED MONOSULCATE POLLEN FROM THE CENOMANIAN, DAKOTA FORMATION, OF CENTRAL USA
Authors: Zavada Michael S. , Dilcher David L.
Published: January 2018

Seven dispersed monosulcate pollen taxa from the Dakota Formation of Minnesota, Nebraska, and Kansas were examined ultrastructurally. Rugubivesiculites rugosus has gymnosperm affinities based on its anasulcate aperture and the presence and nature of the formation of sacci. Stellatopollis sp. has exine sculpturing restricted to taxa with angiosperm affinities and is monosulcate. The affinities of the other five monosulcate taxa are uncertain and the exines are tectategranular. The sulcus in many of the remaining five taxa are flanked by small flange‐like sacci. These five taxa have features found in gymnosperms and also some features of primitive extant angiosperms. The combination of characters of the pollen types presented here does not entirely agree with our current concept of primitive pollen characters as understood from extant ranalean angiosperms.
FORMATION OF HAPLOID EMBRYOIDS OF LARIX DECIDUA: EARLY EMBRYOGENESIS
Authors: von Aderkas P. , Bonga J. M.
Published: January 2018

Callus initiation of sections of megagametophytes of Larix decidua occurs just below the cut surface and is followed by the formation of one or more long protruding cells. The long cells then divide transversely at their tips to yield small cytoplasmically‐dense terminal cells. The latter divide, forming loose aggregates of dense cells, microcalli, which develop long cells that radiate in all directions and divide terminally to produce aggregates of small cells. This long/short cell alternation is repeated a few times. Eventually the aggregates divide in a polarized manner producing files of long cells predominantly in one direction. These loosely bundled long cells form a suspensor‐like structure. The meristematic small cells continue dividing forming a mass of embryonal cells. This early embryoid eventually turns green and produces both a root and shoot. Haploid embryoids are also derived from long cells in which karyokinesis but not cytokinesis occurs, resulting in a four‐nucleate coenocyte. The nuclei migrate to one pole and become surrounded by cell walls. The cells thus formed are the originators of a new embryoid.
COMPETITION BETWEEN SCHIZACHYRIUM SCOPARIUM AND PROSOPIS GLANDULOSA
Authors: Van Auken O. W. , Bush J. K.
Published: January 2018

A competition experiment was carried out in a greenhouse with Schizachyrium scoparium (Michx.) Nash (little bluestem) and seedlings of Prosopis glandulosa Torr. (honey mesquite). The effect of S. scoparium density on the growth of P. glandulosa and the effect of a single P. glandulosa seedling on the growth of various densities of S. scoparium were examined. When P. glandulosa was grown with S. scoparium, there was a significant decrease in P. glandulosa above‐, belowground, and total dry weight at all S. scoparium densities tested. In contrast, P. glandulosa did not cause a significant reduction in S. scoparium dry weight. Root: shoot ratios for both P. glandulosa and S. scoparium increased almost three times from lowest to highest grass density. The number and length of flowering stalks of S. scoparium per plant decreased with increasing density. The presence of P. glandulosa caused a slight nonsignificant reduction of the number and length of S. scoparium flowering stalks. Establishment of P. glandulosa and other woody legumes would probably be low in high glass density and highly productive grasslands.
SEED MORPHOLOGY OF THE SUBFAMILY PITCAIRNIOIDEAE (BROMELIACEAE) AND ITS SYSTEMATIC IMPLICATIONS
Authors: Varadarajan G. S. , Gilmartin A. J.
Published: January 2018

Scanning electron microscopy (SEM) observations of seed samples of 75 species representing fourteen Pitcairnioideae genera combined with some seed developmental and germination data revealed six classes of seed morphology (the Dyckia type, Puya ferruginea type, Puya hamata type, Fosterella type, Navia type and the Brocchinia type). Overall seed shape, nature of the appendage, presence or absence of visible demarcation between the body and appendage, surface cellular pattern and the permanency of the appendage were especially useful for distinguishing the seed types. Taxonomically, seed characteristics are correlated with other features in indicating a close relationship between i) Encholirium and Dyckia, ii) Fosterella and the Guayana Highland generic group (Ayensua, Connellia and Cottendorfia) and iii) Pepinia and Puya, and within the species of Puya hamata complex. Seed morphology suggests an isolated position for Brocchinia within the subfamily. Phylogenetically, seeds of the Fosterella and Puya ferruginea types represent putative homoplasies due to the reversals and parallelisms in different groups. Other seed types are unique to their lineages. Some putative phyletic transformations of the Brocchinia and Navia type seeds correspond with those of the Tillandsioideae and Bromelioideae, respectively.
LEAF REMOVAL AND THE APPARENT EFFECTS OF ARCHITECTURAL CONSTRAINTS ON DEVELOPMENT IN CAPSICUM ANNUUM
Authors: Thomas Lisa P. , Watson Maxine A.
Published: January 2018

The vascular architecture of plants may constrain the pattern of resource movement among organs, resulting in morphological subunits that behave relatively autonomously, particularly with respect to carbon. Systematic and random patterns of leaf removal were imposed on Capsicum annuum plants to examine how architectural constraints may affect the development of sympodial branch systems. Removing leaves within a branch system resulted in a significant decrease in further sympodial growth by that branch, compared to a random pattern of leaf removal or to no removal at all. Data are consistent with the hypothesis that individual branch systems of Capsicum function as integrated physiological units (IPUs). Developmental potential appears to be controlled within these IPUs.
PHYLLOTAXIS THEORIES AND TEPAL‐STAMEN SUPERPOSITION IN BASELLA RUBRA
Authors: Lacroix Christian , Sattler Rolf
Published: January 2018

Instead of alternating as is typical for the majority of flowering plants, the five stamens of Basella rubra are superposed to the five tepals. The first two tepals toward the abaxial side are initiated first, followed by the two tepals toward the adaxial side and the abaxial tepal that may be lagging behind. Stamen inception mirrors that of the petals, i.e., the two stamens toward the abaxial side are initiated first, followed by those toward the adaxial side and the abaxial one that may be lagging behind. Existing phyllotaxis theories do not seem to fully explain this pattern of petal‐stamen superposition. Apart from the Basellaceae, superposition between perianth members and stamens or stamen fascicles occurs in about 13% of all families of flowering plants, although in some of them it is restricted to only a few members. Other floral patterns that also resist explanation in terms of existing phyllotaxis theories are briefly discussed.
PRECIPITATION AS A SOURCE OF ASSIMILABLE NITROGEN: A HISTORICAL SURVEY
Authors: Klein Richard M. , Adamowicz Sue , Perkins Timothy D. , Liedeker Heiko
Published: January 2018

The sources, uptake, and assimilation of nitrogen by plants has a history that dates from the time of the ancient Greeks, and the elucidation of the interlocking questions occupied some of the finest philosophical and scientific minds of Europe for considerably longer than two millenia. Current acidic precipitation, containing a significant amount of nitrogen, has again focused attention on the role of precipitation nitrogen in plant nutrition.
REGENERATION OF THE SUNFLOWER CAPITULUM AFTER CYLINDRICAL WOUNDING OF THE RECEPTACLE
Authors: Hernandez Luis F. , Palmer John H.
Published: January 2018

Using the young capitulum ofHelianthus annuusL., a cylindrical plug of undifferentiated receptacle tissue, 1 mm in diameter, was isolated from lateral communication with the rest of the receptacle surface by a vertical circular wound cut, while retaining continuity with the subapical meristem. Within 24 hr, active cell division was induced at the inner and outer surfaces of the wound and in the receptacle epidermis bordering the wound edges, creating a rounded rim at the top of the wound. Within 3–6 days, floral initials, spaced 133–166μm apart appeared on the flanks of both rims and later on the top of the plug and surrounding receptacle surface. The first formed initials developed into involucral bracts or ray florets and the later ones into disc florets which were organized into contact parastichies, the number of which did not conform with the Fibonacci series. The base of the plug developed into a stem‐like structure completing the regeneration of a fully formed functional capitulum. This operation was demonstrated for two sunflower cultivars and occurred in both long and short daylengths.
REEXAMINATION OF PORE WATER SULFIDE CONCENTRATIONS AND REDOX POTENTIALS NEAR THE AERIAL ROOTS OF RHIZOPHORA MANGLE AND AVICENNIA GERMINANS
Authors: McKee Karen L. , Mendelssohn Irving A. , Hester Mark W.
Published: January 2018

Soil redox potentials and pore water sulfide concentrations on a mangrove island in the Belizean barrier reef system were significantly correlated with the presence of the aerial roots of mangrove trees. Sulfide concentrations were three to five times lower near the prop roots of Rhizophora mangle (red mangrove) and the pneumatophores of Avicennia germinans (black mangrove) than in adjacent (≤ 1 meter away) unvegetated sediment. Soil redox potentials were also significantly higher near the aerial roots. A comparison of the two species revealed that sulfide concentrations in the rhizosphere of R. mangle were as low as that of A. germinans. However, sulfide concentrations in areas occupied by the black mangrove were variable and a function of pneumatophore density. The occurrence of an oxidized rhizosphere around the roots of both species suggests that the adult trees are equally capable of exploiting reduced sediments as long as their respective pathways for root aeration are functional.
OCCURRENCE OF PREDATORY AND FUNGIVOROUS MITES IN LEAF DOMATIA
Authors: Pemberton Robert W. , Turner Charles E.
Published: January 2018

Domatia are small invaginations and hair tufts usually found at vein junctions on the undersides of leaves in many woody dicots. Domatia of 32 plant species (of worldwide origin from 18 families) growing in California, Hawaii, and Costa Rica were examined for mites. Domatia of 31 of 32 (97%) of these plants contained mites, and 24 of 32 (75%) contained mite eggs. Mites were found within the domatia of 48% of the sampled leaves. The domatia of 26 of 31 (84%) plants had mite species considered beneficial (primarily in the families Phytoseiidae and Tydeidae, but also Bdellidae, Cheyletidae and Stigmaeidae), while 6 of 31 (19%) had mite species considered harmful (Tenuipalpidae and Eriophyidae). Based on these findings (and in part upon Lundström's 1887 domatia theory), we hypothesize the existence of a widespread facultative mutualism between plants with leaf domatia and beneficial mites: leaf domatia serve as shelters and nurseries for mites which in turn eat phytophagous arthropods and pathogens using the plants. This proposed mutualism could be of importance to agriculture since domatia are known to occur in some crop plants, including coffee, grape, and walnut.