bluuebunny/crossref_metadata_2025 huggingface dataset:
CAESALPINIA SUBGENUS MEZONEURON (LEGUMINOSAE, CAESALPINIOIDEAE) FROM THE TERTIARY OF NORTH AMERICA
Authors: Herendeen Patrick S. , Dilcher David L.
Published: January 2018

Legume fruits from the Eocene of Tennessee and Wyoming and the Miocene of Idaho are described and assigned to Caesalpinia subgenus Mezoneuron (Caesalpinioideae), an extant Paleotropical taxon that does not occur in North or South America today. Morphological and anatomical details of the fruits are used in evaluating their systematic relationships. The features of the fossil fruits are accommodated only within this extant subgenus. These fossils represent the only reliable known occurrence of C. subgenus Mezoneuron in the paleobotanical record. These fossils suggest that subgenus Mezoneuron was distinct from subgenus Caesalpinia by the Middle Eocene. Further, they document the widespread occurrence of this currently Paleotropical group for at least 30 million years in North America.
ULTRASTRUCTURAL STUDY ON SPORE WALL MORPHOGENESIS IN LYCOPODIUM CLAVATUM (LYCOPODIACEAE)
Authors: Uehara Koichi , Kurita o
Published: January 2018

Spore wall morphogenesis of Lycopodium clavatum was observed by transmission electron microscopy. The spore plasma membrane indicates the reticulate spore sculpture shortly after meiosis. The mature spore wall of this species consists of two layers, inner endospore and outer exospore. There is no perispore in the sporoderm of this species. The exospore formation begins during the tetrad stage; and this layer is divided into two distinct sublayers, an outer lamellar layer and an inner granular layer. The lamellar layer is formed on the sculptured spore plasma membrane. Additional lamellae attach to this layer in a centripetal direction. For that reason, this layer may be derived from spore cytoplasm. The granular layer is formed only in the proximal region following lamellar layer formation, and it also may be derived from spore cytoplasm. The endospore is formed lastly and seems to be derived from spore cytoplasm as well. Accordingly, the spore sculpture of this species may be under the genetic control of the spore nucleus.
IDENTIFICATION OF PROCAMBIUM IN THE PRIMARY ROOT OF TRIFOLIUM PRATENSE (FABACEAE)
Authors: Mueller Richard J.
Published: January 2018

Histochemical and morphometric analyses were used to identify and define an early stage of procambial differentiation in 1.5–2.0‐cm‐long (48 hr after germination) primary roots of Trifolium pratense L. Esterase activity was used as a histochemical marker for early differentiation of procambium. Morphometric analysis of cell length and width as a function of distance from the root cap junction was performed on the same tissue using brightfield and Nomarski DIC optics. This combination of techniques allowed the identification of esterase activity in both the cell wall and cytoplasm and permitted the determination of the exact location, size, and shape of the histochemically stained cells within the apex. Esterase activity identified the proendodermis and procambial cylinder (six to seven cells in diameter) two to three cells proximal to the root cap junction. In this system, esterase activity proved to be an earlier marker for procambial differentiation than morphometric or cytological changes. It is suggested that these techniques will be useful in characterizing procambial pattern development in more complex shoot systems.
MORPHOLOGY AND TAXONOMIC POSITION OF SUCKLEYA SUCKLEYANA (CHENOPODIACEAE)
Authors: Chu G. L. , Stutz H. C. , Sanderson S. C.
Published: January 2018

Contrary to taxonomic descriptions, female flowers of Suckleya suckleyana have four perianth segments rather than two bracts. Consequently, Suckleya suckleyana belongs in the tribe Chenopodieae, family Chenopodiaceae, instead of tribe Atripliceae. Since it is the only member of tribe Chenopodieae with unisexual flowers and superior radicles, it is proposed that it be assigned to a new subtribe, Suckleyinae.
EFFECTS OF CO2 ENRICHMENT ON THE GROWTH AND MORPHOLOGY OF A NATIVE AND AN INTRODUCED HONEYSUCKLE VINE
Authors: Sasek Thomas W. , Strain Boyd R.
Published: January 2018

Japanese honeysuckle (Lonicera japonica Thunb.), introduced to the United States, and the native coral honeysuckle (Lonicera sempervirens L.) were compared to determine how intrinsic differences in their growth characteristics would affect their response to atmospheric carbon dioxide enrichment. Plants of both species grown from cuttings were harvested after 54 days of growth in controlled environment growth chambers at 350, 675, or 1,000 μl/liter CO2. The biomass of Japanese honeysuckle was increased 135% at 675 μ∗∗∗l/liter CO2 and 76% at 1,000 μl/liter CO2 after 54 days. Morphologically, the main effect of CO2 enrichment was to triple the number of branches and to increase total branch length six times. Enhanced and accelerated branchingalso increased total leaf area 50% at elevated CO2 concentrations. In coral honeysuckle, total biomass was only 40% greater in the elevated CO2 treatments. Branching was quadrupled but had not proceeded long enough to affect total leaf area. Main stem height was increased 36% at 1,000 μl/liter CO2. The much less significant height response of other woody erect growth forms suggests that vines may increase in importance during competition if atmospheric CO2 concentrations increase as predicted. The impact of Japanese honeysuckle in the United States may become more serious.
AMPHISTOMY AS AN ADAPTATION TO HIGH LIGHT INTENSITY IN AMBROSIA CORDIFOLIA (COMPOSITAE)
Authors: Mott Keith A. , Michaelson Odette
Published: January 2018

Adaptation to high light intensity in Ambrosia cordifolia (Compositae) involved an increase in leaf thickness, photosynthetic capacity, and maximum stomatal conductance. In addition, leaves produced at high light intensities were amphistomatous, but those produced at low light intensities were hypostomatous. Although stomatal density on the upper surface was increased with increasing light intensity, the total stomatal density (upper + lower surfaces) was not substantially affected by light intensity because the density of stomata on the lower surface was reduced at high light intensities. The possible value of amphistomy in reducing diffusional limitations to photosynthesis in thick, high photosynthetic‐capacity leaves is discussed.
IN VIVO MAGNETIC RESONANCE IMAGING OF BLECHNUM FERNS: CHANGES IN T1 AND N(H) DURING DEHYDRATION AND REHYDRATION
Authors: Veres John S. , Johnson G. Allan , Kramer Paul J.
Published: January 2018

The order, rate, and extent with which plant tissues dehydrate during water stress and rehydrate remains largely unknown. In vivo magnetic resonance imaging was used at seven Tesla to measure changes in degree of water binding and relative water content (through T1 and N[H] changes) of Blechnum unilaterale stem regions as water stress developed and was relieved. Spin‐lattice relaxation times (T1s) of B. unilaterale stem regions were found to be positively linearly correlated with water potential. In the well‐watered state, the longest T1s were associated with the stem margin, followed by cortical parenchyma, pith parenchyma, and vascular bundles. During water stress, T1 values of the stem margin, cortical parenchyma, and pith parenchyma converged. After rehydration, T1s returned nearly to initial values. As indicated by a decrease in relative spin density (N[H]), the stem margin and cortical parenchyma began to lose water first during dehydration with the rate and extent of water loss being greatest for the stem margin. Later, water loss occurred from all regions; most rapidly and to a greater extent from the stem margin and vascular bundles. During water stress, N(H) of stem regions converged to a common value. Order of rehydration of stem regions was the same as order of dehydration. This study demonstrates that MR imaging can be used as a noninvasive tool for examining changes in the degree of water binding and water content of stem regions in live plants.
PATTERNS IN LEAF MORPHOLOGY AND PHOTOSYNTHESIS IN SHOOTS OF SASSAFRAS ALBIDUM (LAURACEAE)
Authors: de Soyza Amrita G. , Kincaid Dwight T.
Published: January 2018

Trees of Sassafras albidum (Nuttall) Nees. display leaves that fall into discrete categories of form. Unlobed leaves, with undissected margins, predominate at proximal and distal nodes of shoots, while lobed leaves are most common at intermediate nodes. In this study we investigated the hypothesis that shoots of sassafras respond to environmental changes over the growing season by generating predictable nodal patterns for leaf morphology and physiology. We recorded leaf shape category and measured leaf surface area, node number, chlorophyll content, nitrogen content, and photosynthesis in four trees. Over 1,000 measurements of photosynthesis were made in situ, using the LI‐Cor LI 6200 portable photosynthesis system. The two trees growing under heavy shade had few lobed leaves (2.0% and 18.8%) and often had negative carbon balance, with positive net photosynthesis occurring during sun flecks. The two trees growing in more open conditions had many more lobed leaves (56.3% and 61.0%) and higher, less variable net photosynthetic rates. As indicated by chlorophyll and nitrogen contents, the highest leaf photosynthetic rates occurred at intermediate nodes (nodes six to nine), and this was shifted distally along the shoot during the growing season. Leaves at intermediate nodes also had the largest surface areas and the greatest frequency of lobing. In comparative experiments with models, lobing was shown to enhance free‐convectional heat loss relative to unlobed leaves of the same surface area. Due to their large surface area, these leaves also have the highest rates of whole leaf photosynthesis. Under conditions of equivalent photosynthetically active radiation, lobed leaves had higher rates of net photosynthesis than did unlobed leaves. We conclude that shoots of sassafras produce groups of leaves with predictably different morphological and physiological specializations.
POSTFERTILIZATION CHANGES IN OVULES OF MONOTROPA UNIFLORA L. (MONOTROPACEAE)
Authors: Olson A. Randall
Published: January 2018

Monotropa uniflora is an achlorophyllous angiosperm consisting of a mycorrhizae‐dependent root system that produces floriferous, aerial shoots. Each of the numerous, minute ovules is anatropous, unitegmic, and contains a Polygonum type female gametophyte. Following double fertilization, a lipid‐rich, cellular endosperm develops in association with both chalazal and micropylar haustoria. The vacuolate zygote elongates prior to a cytoplasmically unequal division resulting in a small terminal cell subtended by a larger, vacuolate basal cell. The basal cell eventually degenerates, isolating the terminal cell which is completely surrounded by endosperm. The terminal cell undergoes a cytoplasmically equal transverse division resulting in a two‐celled embryo embedded in endosperm. In final stages of seed maturation, lipids decrease and reserve proteins increase in the cytoplasm of both the endosperm and embryo. The morphological reduction of the mature embryo may be associated with a specialized mode of nutrition.
ARTIFICIAL HYBRIDIZATION IN HAWAIIAN WIKSTROEMIA (THYMELAEACEAE)
Authors: Mayer Stephanie S.
Published: January 2018

Crosses were performed within and between 19 Hawaiian populations of the mostly dioecious woody shrub Wikstroemia. These populations are from a variety of habitats on the six major islands and are morphologically diverse. The populations are referrable to eight of the 12 species recognized by Peterson. Almost all hybrid combinations produced seeds, and seed‐set was not significantly different among three categories of hybrids (within population, between populations on the same island, and between populations on different islands). F1s from many of the crosses were vigorous and fertile, leading to the conclusion that these populations are not reproductively isolated from each other and the assumption that they are genetically very similar. Natural hybridization was difficult to detect because the species described by Peterson intergrade morphologically and ecologically. The crossability and interfertility of populations of Wikstroemia may be explained by one or more of the following hypotheses: 1) recency of colonization, 2) the founder effect, 3) lack of selection for barriers to interbreeding, and 4) gross morphological changes without associated large genetic changes.
OSMOPHORES, FLORAL FEATURES, AND SYSTEMATICS OF STANHOPEA (ORCHIDACEAE)
Authors: Curry Kenneth J. , McDowell Lorraine M. , Judd Walter S. , Stern William Louis
Published: January 2018

The floral fragrance glands (osmophores) of 18 species of Stanhopea and Sievekingia were examined through a series of developmental studies at light and electron microscope levels including late bud stages through postanthesis. Various characters were identified to be of potential systematic value and were recorded for each species. These characters included: texture of the osmophore surface, number of distinct cell layers comprising the osmophore, nature of lipid inclusions in osmophore cells, and presence or absence of plastoglobuli in osmophore amyloplasts. These characters were combined with traditional features of floral lip morphology for cladistic analysis. Sievekingia was the postulated outgroup. Stanhopea ecornuta showed the largest number of plesiomorphic characters. Stanhopea pulla, S. annulata, and S. Candida were only slightly more derived. Stanhopea anfracta, S. gibbosa, S. martiana, S. oculata, S. radiosa, S. ruckeri, S. saccata, S. shuttleworthii, S. tigrina, S. vasquezii, and S. wardii form a monophyletic group that can be recognized by a labellum with an articulated epichile and a bicornuate mesochile (or hypochile). Stanhopea tricornis may be a hybrid between a species of Sievekingia and Stanhopea.
PALEOCENE DICOTYLEDONOUS TREES FROM BIG BEND NATIONAL PARK, TEXAS: VARIABILITY IN WOOD TYPES COMMON IN THE LATE CRETACEOUS AND EARLY TERTIARY, AND ECOLOGICAL INFERENCES
Authors: Wheeler E. A.
Published: January 2018

Paraphyllanthoxylon abbottiin. sp. and cf.Plataninium haydeniiFelix from the Paleocene Black Peaks Formation, Big Bend National Park, Texas, are the first Paleocene dicotyledonous woods described from North America. Both represent wood types common in the Cretaceous. There are 30 logs ofParaphyllanthoxylon abbottii;it is rare that a single locality has such as large number of petrified dicotyledonous logs with a similar structural pattern, and the variability in mature wood structure can be documented.Paraphyllanthoxylon abbottiihas a combination of features that occurs in many dicotyledonous families, but it is most similar to genera of Burseraceae. The Big BendParaphyllanthoxylontrees lack distinct growth rings, which suggests they grew in a climate without marked seasonality; they have high (10–74) vulnerability indices; such high values occur in extant tropical trees. The type species ofParaphyllanthoxylon, P. arizonenseBailey was reexamined, and its quantitative features are described.AplectotremasSerlin of Albian age from the Edwards Limestone has anatomy likeParaphyllanthoxylon,and most probably is wood from a tree. The wood designated cf.Plataninium haydeniiFelix resembles extant Platanaceae but differs in having exclusively scalariform perforation plates. Comparison of this wood with other platanoid woods suggests that in platanoid woods there has been a shortening of vessel elements and a decrease in the frequency of scalariform perforation plates from the Cretaceous through the Tertiary. These changes are consistent with the Baileyan model for specialization in tracheary elements.
BIAS IN INHERITANCE OF CHLOROPLAST DNA AND MECHANISMS OF HYBRIDIZATION BETWEENWIND‐ AND INSECT‐POLLINATED EUPATORIUM (ASTERACEAE)
Authors: Sullivan Victoria I. , Neigel Joseph , Miao Bomao
Published: January 2018

Hybrids of the wind‐pollinated E. capillifolium and the insect‐pollinated E. serotinum were found to occur in the Coastal Plain of Louisiana, Mississippi, and southern Arkansas and on the Piedmont in three locations. Interspecific cross‐pollination occurs when wind causes the flexible flowering branches of E. capillifolium to whisk over the stiff upright branches of E. serotinum plants. Interspecific pollen was found to be captured by E. serotinum more effectively than by E. capillifolium. However, analysis of cpDNA of natural field hybrids indicated that most were maternally descended from E. capillifolium. This latter bias can be explained by the far greater number of flowers, and thus greater seed producing capacity, of E. capillifolium relative to E. serotinum. Morphological variability observed among field hybrids suggests that backcrossing has occurred; however, field hybrids and progeny grown from field hybrid achenes generally had low pollen stainability, irregular meiosis, and reduced achene set. Furthermore, field hybrids were found to have a chromosome number of 2n = 20, like the parental species, whereas progeny grown from field hybrids had deficiencies and duplications of chromosome numbers. Because these chromosome number deviations were not seen in field hybrids it is logical to suggest that either they are F1s, or that strong selective forces in the field eliminated the progeny of hybrids with deficiencies and duplications.
CHLOROPLAST‐DNA VARIATION IN TELLIMA GRANDIFLORA (SAXIFRAGACEAE)
Authors: Soltis Douglas E. , Mayer Michael S. , Soltis Pamela S. , Edgerton Michael
Published: January 2018

Tellima grandiflora, a herbaceous, diploid (2n= 14) perennial, is distributed from the peninsula and panhandle of Alaska to central California. Restriction site variation of chloroplast DNA was surveyed in 51 populations representing the geographic range ofT.grandiflorausing 20 endonucleases. Two well‐differentiated clades of populations differing by 19 restriction site mutations and several length mutations are geographically structured. A northern group comprises populations from Alaska to central Oregon; populations from central Oregon to San Francisco, California, form a southern group. The southern lineage of the monotypicTellimaappears to have obtained its chloroplast genome via ancient hybridization with a species ofMitella.Although northern and southern lineages have well‐differentiated chloroplast genomes, populations ofT. grandiflorashow a high degree of genetic similarity of nuclear‐encoded allozymes; furthermore, no apparent morphological differences characterize the lineages. Significantly, several populations ofT. grandiflorathat possess the typical southern chloroplast genome also occur disjunctly on Prince of Wales Island, Alaska, and the Olympic Peninsula, Washington. Because both areas are proposed glacial refugia, we suggest that past glaciation may have created discontinuities in the geographic distribution ofT. grandiflora.Following glaciation, migration of once‐isolated populations possessing different chloroplast genomes resulted in the formation of a continuous geographic distribution with a major organellar discontinuity. Additional support for this hypothesis is provided by the presence of well‐differentiated northern and southern chloroplast DNA lineages inTolmiea menziesii, a species having a geographic distribution and life history traits similar to those ofTellima.
EMBRYONIC GENETIC LOAD IN THE HIGHBUSH BLUEBERRY, VACCINIUM CORYMBOSUM (ERICACEAE)
Authors: Krebs Stephen L. , Hancock James F.
Published: January 2018

Hand‐pollinations of 28 autotetraploid V. corymbosum accessions from a single population resulted in lower self‐ than outcross seed set. Fertility varied widely, ranging from clones that were effectively female sterile to individuals with high seed yields in both matings. Self‐ and outcross fertility were highly correlated. A genetic load model was invoked to explain these phenomena. Reduced self‐fertility was attributed to homozygosity for sublethal mutations at loci controlling embryo development, or to loss of heterotic interactions at these loci. Near zero cross‐fertility in some clones may be evidence of partially dominant mutational load. Estimates of the number of lethal equivalents per zygote carried by individuals in this population ranged from 2.2 to 20.4, with a mean of 9.6. Embryonic genetic load at the individual level was significantly correlated with heterozygosity at nine enzyme loci. Low pollen viability and reduced receptivity to pollen from any source were also noted in the low fertility genotypes. It is suggested that gametic, gametophytic, and embryonic development are symptomatic of the amount of genetic load carried by individuals.
EXPERIMENTAL ASSESSMENT OF REPRODUCTIVE INTERACTIONS BETWEEN SYMPATRIC ASTER AND ERIGERON (ASTERACEAE) IN INTERIOR ALASKA
Authors: Armbruster W. Scott , McGuire A. David
Published: January 2018

Erigeron glabellus and Aster sibiricus have similar flowers, share pollinators, but bloom sequentially in interior Alaska. Both species depend on insect pollination for seed set: the Erigeron is self‐incompatible, and the Aster is apparently self‐compatible but allogamous. To test the hypothesis that sequential blooming is maintained by natural selection generated by reproductive interference, we manipulated the flowering time of Erigeron, forcing it to bloom simultaneously with Aster, and measured female fecundity in both species. We found no evidence of reduced female fecundity in either species caused by the presence of the sympatric “competitor” or by artificial pollination with the heterospecific pollen prior to conspecific pollination. Two‐species mixtures of simultaneously blooming Aster and Erigeron experienced significant interspecific visitation, which may, under natural conditions, cause loss of pollen to alien stigmas and depressed male fecundity, at least in Erigeron. We found no evidence that sequential blooming in Erigeron and Aster is maintained by depressed female fecundity through pollinator sharing. If sequential blooming is maintained by natural selection, it seems more likely to be the result of selection generated by depressed male fitness through pollen loss to alien stigmas.
BOTRYOPTERIS FORENSIS (BOTRYOPTERIDACEAE), A TRUNK EPIPHYTE OF THE TREE FERN PSARONIUS
Authors: Rothwell Gar W.
Published: January 2018

Basal parts of Botryopteris forensis have been discovered rooted within the mantle of the tree fern Psaronius. Specimens occur in Upper Pennsylvanian coal balls from near Steubenville, Ohio, USA. The Botryopteris stems branch profusely, and these shoots are intertwined with the Psaronius roots near the surface of the mantle. They also produce adventitious roots that extend among the Psaronius roots. This material demonstrates that B. forensis was a trunk epiphyte, rather than a rhizomatous terrestrial fern. The B. forensis plant is interpreted to have branched continuously, to ramify, and to maintain itself at the periphery of the growing mantle of Psaronius roots. A new reconstruction of B. forensis is offered showing the large, globose fructifications hanging pendulously from horizontal fronds on emergent shoots. Epiphytes and lianas are common on the trunks of Psaronius, indicating that some Marattiales did not produce leaf skirts.
PHOTOSYNTHETIC CHARACTERISTICS OF C3‐C4 INTERMEDIATE FLAVERIA FLORIDANA (ASTERACEAE) IN NATURAL HABITATS: EVIDENCE OF ADVANTAGES TO C3‐C4 PHOTOSYNTHESIS AT HIGH LEAF TEMPERATURES
Authors: Monson Russell K. , Jaeger Charles H.
Published: January 2018

Measurements of leaf gas exchange were conducted in situ for the C3‐C4 intermediate plant Flaveria floridana. Leaves exhibited measurable CO2 assimilation at atmospheric CO2 concentrations as low as 20 μmol/mol. This result demonstrates that the low CO2 compensation points observed in past studies of greenhouse‐grown C3‐C4 intermediate plants also exist in plants growing in their natural habitat. Photosynthesis rates in F. floridana were near their maximum at intercellular CO2 concentrations as low as 112 μmol/mol. The existence of near‐maximum photosynthesis rates at such low intercellular CO2 concentrations is interpreted as evidence for the existence of a CO2‐concentrating mechanism in F. floridana. Such a mechanism would also explain the observed lack of response in photosynthesis rates to reductions in stomatal conductance and intercellular CO2 concentration as the leaf‐to‐air water vapor concentration gradient is increased. Photosynthetic rates were relatively high at leaf temperatures between 35 and 40 C, compared to most C3 plants. At midday during May, when leaf temperatures were between 35 and 42 C, F. floridana leaves exhibited photosynthesis rates that were four times higher than a sympatric C3 species (Eustoma exaltatum) of similar growth form and ecological habit. The high photosynthesis rates at high leaf temperatures in F. floridana were not due to higher leaf nitrogen contents, but rather to its reduced rate of photorespiration. These results confirm that C3‐C4 intermediate photosynthesis can provide plants with an advantage at high leaf temperatures, compared to C3 plants.
HOMEOSIS IN THE FLOWERS OF THE ZINGIBERALES
Authors: Kirchoff Bruce K.
Published: January 2018

Homeosis has played an important role in the evolution of the flowers of the Zingiberales, especially those of the Ginger Group. In the Zingiberaceae, two members of the outer androecial whorl are replaced by a lip, and two members of the inner androecial whorl are replaced by petaloid staminodes. Most of the androecium of the Costaceae has also been replaced by petaloid structures, and the single fertile stamen is often attached to an enlarged petaloid “filament.” The Cannaceae and Marantaceae have one‐half of one fertile anther and three to four variously modified staminodes. In contrast, homeosis has played a minor role in floral evolution of the Banana Group. Only in the Heliconiaceae has a stamen been replaced by a staminode. In none of the families of the Zingiberales do the staminodes assume the total “form or character” of any perianth members. Because of this, it is reasonable to extend the definition of homeosis to include replacement by an organ like, but not identical to, some other part of the plant.
THE ELASTIC MODULI AND MECHANICS OF POPULUS TREMULOIDES (SALICACEAE) PETIOLES IN BENDING AND TORSION
Authors: Niklas Karl J.
Published: January 2018

Changes attending leaf development in the mechanical behavior and elastic moduli of the petioles of Populus tremuloides Michx. were examined in terms of total leaf weight (Wt), lamina and petiole weight (Wl and Wp), petiolar length (L), and lamina surface area (A). A primary concern was the extent to which two elastic moduli (Young's modulus E and the shear modulus G) of petioles changed over time and were correlated with one another. E and G were measured by means of multiple resonance frequency spectra, and together with the dimensions of cross sections through petioles, these two elastic moduli were used to estimate the stiffness of petioles in simple bending and torsion. Petiolar bending was predicted by means of a model incorporating expressions for both the bending stiffness (El) and torsional rigidity (GJ), where I is the second moment of area and J is the torsional constant. The predictions from these models were compared to observed petiolar bendings due to Wl. Additionally, the frequency of the oscillatory motion of leaves (placed in a wind tunnel with a 1 m sec‐1 ambient wind speed, directed normal to the blade of the leaf) was determined. Results indicate that L, A, Wl, Wp, and Wt were positively correlated with the age of leaves (crudely estimated as a function of leaf plastochron index, LPI); these morphometric parameters were also correlated with the magnitudes of E and G. Also, G was positively and linearly correlated with E, and was, on the average, an order of magnitude less than E. EI and GJ were positively correlated with LPI. The relationships among E, G, EI, C and Wl, Wp, Wt are discussed in terms of leaf allometries.
EFFECTS OF SNOWPACK ON TIMING AND ABUNDANCE OF FLOWERING IN DELPHINIUM NELSONII (RANUNCULACEAE): IMPLICATIONS FOR CLIMATE CHANGE
Authors: Inouye David W. , McGuire A. David
Published: January 2018

Delphinium nelsonii is an early‐blooming herbaceous perennial of montane western North America, which we studied in dry subalpine meadows in the Colorado Rocky Mountains. We examined the effects of variation in annual snowfall between 1973 and 1989 on the timing and abundance of flowering. During years of lower snow accumulation, D. nelsonii plants experienced colder temperatures between the period of snowmelt and flowering. Also, flowering was delayed, floral production was lower, and flowering curves were more negatively skewed; damage during floral development probably occurred in years of low snowfall. If climate change results in decreased mean annual snowfall for the Rocky Mountains, then the seed production of D. nelsonii will probably be adversely affected. Decreased snowfall may also indirectly lower the seed production of later‐blooming species by decreasing populations of bumblebees and hummingbirds that forage on D. nelsonii flowers. Decreased snowfall has the potential to reduce the number and relative proportions of species in the herbaceous flora in our study area.
THE PHYSICAL AND CHEMICAL ENVIRONMENT OF THE DEVELOPING EMBRYO OF PINUS RESINOSA
Authors: Gates Judy C. , Greenwood Michael S.
Published: January 2018

The relationship between changes in soluble protein, hexose sugar, total lipid concentration, and osmotic potential occurring in gametophytic supernatant of Pinus resinosa Ait. during in vivo embryogenesis was measured. The effects of varying sucrose levels of culture medium on in vitro embryo and gametophyte development were examined. Increases in embryo volume, and fresh and dry weight of the female gametophyte during in vivo embryogenesis coincide with increasing levels of soluble protein, hexose sugar, and total lipid in the gametophytic supernatant. In contrast, osmotic potential of the supernatant increased only slightly between the zygote and proembryo stages of embryo development, and remained constant thereafter. Gametophytes plus embryos grown in vitro achieved dry weights approaching those of in ovulo gametophytes on media containing levels of sucrose up to 21%. Gametophytes on media with sucrose concentrations up to 21% also resembled normal in ovulo gametophytes in appearance. However, embryo development appeared to be suspended on treatment media containing from 9% to 21% sucrose, while embryos degenerated on media with constant sucrose levels of 3% and 6%. A treatment medium containing approximately 12% sucrose would provide an osmotic environment that duplicates that found in ovulo. While greater sucrose levels promoted more normal gametophyte development in Pinus resinosa, we failed to achieve complete development of the embryo in vitro. Conclusions and implications drawn from these results are discussed.
TRIBAL PLACEMENT OF MARSHALLIA (ASTERACEAE) USING CHLOROPLAST DNA RESTRICTION SITE MAPPING
Authors: Watson Linda E. , Jansen Robert K. , Estes James R.
Published: January 2018

The examination of morphological traits has failed to resolve the tribal placement of Marshallia. Suggested relationships for this anomalous genus have, at various times, included Eupatorieae, Heliantheae, Vemonieae, and Inuleae. Chloroplast DNA restriction site mapping, using Bamadesiinae (Mutisieae) as the outgroup, revealed 981 restriction site mutations, 332 of which were phylogenetically informative, for 60 genera representing 15 tribes of Asteraceae. Wagner parsimony produced 36 equally parsimonious tress of 729 steps, and Dollo parsimony produced 34 equally parsimonious trees of 759 steps. Monophyletic groups, resulting from the Wagner analysis, were further tested with the bootstrap method. The placement of Marshallia in the Heliantheae‐Tageteae‐Coreopsideae‐Eupatorieae complex was consistent for all trees produced. Tageteae and Coreopsideae form the sister group to paraphyletic Heliantheae, with Marshallia sharing its most recent common ancestor with Galinsoga, Palafoxia, and Bahia. The Eupatorieae form a monophyletic clade that is derived from helianthoid ancestors.
REPRODUCTIVE COSTS OF SELF‐POLLINATION IN IPOMOPSIS AGGREGATA (POLEMONIACEAE): ARE OVULES USURPED?
Authors: Waser Nickolas M. , Price Mary V.
Published: January 2018

In common with many cosexual angiosperms, the hummingbird‐pollinated montane herb Ipomopsis aggregata (Polemoniaceae) is likely to experience self‐pollination. Does this incur a fecundity cost even in such a highly self‐sterile (presumably self‐incompatible) species? Histological studies showed that self pollen germinates, and its tubes penetrate ovules almost as often as those of outcross pollen. Ovules penetrated by self tubes are especially likely to show milky callose occlusion 24–48 hr after pollination, and several observations suggest an association between occlusion and degeneration. Compared to flowers receiving only outcross pollen, seed set was reduced by 42% on average when self pollen was applied along with outcross, either by hand (in emasculated flowers) or by natural autodeposition (in unemasculated flowers). Reductions were statistically indistinguishable whether self pollen was applied 9 hr before outcross pollen, or at the same time. Unemasculated flowers accumulated substantial self pollen loads, and this autodeposition persisted when flowers were probed to mimic hummingbird visitation. Geitonogamy also is substantial, judging from field estimates of pollen transfer. Thus natural self pollen deposition may be sufficient to “usurp” ovules that otherwise could mature. In this light, late‐acting self‐rejection in I. aggregata seems decidedly less efficient than an early‐acting system that would block pollen germination or tube growth.
CHLOROPLAST DNA VARIATION WITHIN AND AMONG GENERA OF THE HEUCHERA GROUP (SAXIFRAGACEAE): EVIDENCE FOR CHLOROPLAST TRANSFER AND PARAPHYLY
Authors: Soltis Douglas E. , Soltis Pamela S. , Collier Trace G. , Edgerton Michael L.
Published: January 2018

The Heuchera group (Saxifragaceae) comprises Bensoniella, Conimitella, Elmera, Heuchera, Lithophragma, Mitella, Tellima, Tiarella, and Totmiea. Earlier studies employing morphology, karyology, and flavonoid chemistry indicated that these genera form a natural group, but failed to resolve relationships among them. Restriction site analysis of chloroplast DNA (cpDNA) suggests that Bensoniella, Tolmiea, and Lithophragma are close allies and form the sister group of a large clade containing the remaining six genera. Mitella and Heuchera are both paraphyletic based on cpDNA data. cpDNA data, in conjunction with morphological and allozyme data, suggest at least four examples of intersectional hybridization and subsequent chloroplast capture in Heuchera. Several of these events may be explained via a stepping stone model in which the chloroplast genome of a species was captured by a second species, and then ultimately by a third taxon. Two well‐differentiated groups of Tellima populations were detected: one group has a unique chloroplast genome characterized by nine autapomorphies, and the second group has a chloroplast genome identical to that found in M. trifida and M. diversifolia. cpDNA and allozyme data suggest that some Tellima populations probably obtained their chloroplast genome via intergeneric hybridization with M. trifida, M. diversifolia, or the ancestor of these taxa. The occurrence of intergeneric chloroplast transfer in some populations of Tellima, as well as extensive intersectional chloroplast capture in Heuchera, not only suggests caution in the use of cpDNA restriction site data in phylogenetic reconstruction, but also demonstrates again the importance of adequate sampling of conspecific populations. If the intergeneric relationships in the Heuchera group suggested by cpDNA analysis are accurate, fundamental questions arise regarding the validity of certain morphological traits as good taxonomic characters in Saxifragaceae. Furthermore, significant taxonomic changes at the generic level would be necessary.
RIBOSOMAL DNA LENGTH POLYMORPHISMS WITHIN POPULATIONS OF XYLARIA MAGNOLIAE (ASCOMYCOTINA)
Authors: Gowan Sharon P. , Vilgalys Rytas
Published: January 2018

Xylaria magnoliae forms abundant conidial and sexual fruiting structures on the fallen strobili of Magnolia spp. throughout the southeastern United States. Populations of X. magnoliae may be identified as isolates originating from a single strobilus, among different strobili from different host trees, and different host tree localities. We examined the stratified structure of X. magnoliae populations by analysis of their ribosomal DNA restriction patterns. A sample of 48 single‐conidial isolates was obtained from strobili of both Magnolia grandiflora and M. fraseri in the piedmont and mountains of North Carolina and Georgia. Southern blotting experiments revealed considerable variation in rDNA lengths between and within different isolates. Although a single rDNA phenotype usually dominates within a particular collecting locality, different phenotypes were also observed within a locality and even between isolates obtained from a single strobilus. Some rDNA restriction phenotypes are distributed over localities separated by up to 400 km. These results suggest a fine‐grained population structure for X. magnoliae, together with the potential for genetic exchange and dispersal between widely separated localities.
CROSSING STUDIES IN CYPHOMANDRA (SOLANACEAE) AND THEIR SYSTEMATIC AND EVOLUTIONARY SIGNIFICANCE
Authors: Bohs Lynn
Published: January 2018

A crossing program involving eight species of Cyphomandra was instituted to elucidate systematic relationships between the taxa and evolutionary mechanisms operating in the genus. The results show that gametophytic self‐incompatibility is widespread in Cyphomandra. Pollen tubes were able to reach the ovules in nearly all interspecific crosses. Most of these crosses failed, however, indicating that postzygotic barriers are important in reproductive isolation. Only five of 44 interspecific combinations attempted have produced viable seeds. F1 plants have been evaluated from three of the five hybrid combinations: C. betacea × acuminata, C. uniloba × betacea, and C. corymbiflora × diploconos. All three hybrid combinations show reduced fertility as compared to the parents, apparently caused in part by differences in chromosome structure between parent species. Crossing success was congruent with morphological similarity in C. betacea, C. acuminata, and C. uniloba, but not in C. corymbiflora and C. diploconos. External isolating mechanisms such as geography, ecology, phenology, and pollinator specificity may also operate to maintain species integrity in nature.
DEVELOPMENTAL DYNAMICS OF ARBORESCENT LYCOPHYTES—APICAL AND LATERAL GROWTH IN STIGMARIA FICOIDES
Authors: Rothwell Gar W. , Pryor Janelle S.
Published: January 2018

Meristematic activity in Stigmaria ftcoides is interpreted from a combination of historical information and newly developed data on stelar diameter, wood production, and morphology of the apex. Many specimens of Stigmaria preserved as mold/casts display little or no recognizable change in the width of the stelar groove between successive forks. Thickness of the xylem cylinder in permineralized axes of similar diameters also is relatively uniform. Over a distance of 1.5 m along one axis the mean number of tracheids per radial row diminishes from 56 to 46 toward the apex. While this is a statistically significant decrease, in biological terms it is consistent with the reduction in primary growth that one would expect in a zone of apoxogenesis. Coupled with our knowledge of the morphology of the apex, these data allow us to interpret radially aligned tracheids in the steles of most stigmarian axes as having been produced largely from the action of a primary thickening meristem, rather than from a secondary vascular cambium as commonly believed.
SPORE MORPHOLOGY OF ANEMIA, MOHRIA, AND CERATOPTERIS (FILICALES)
Authors: Dettmann Mary E. , Clifford H. T.
Published: January 2018

Spores of the ferns Anemia and Mohria (Schizaeaceae) and Ceratopteris (Pteridaceae) are surveyed with light microscopy and scanning and transmission electron microscopy. In each genus the spores are trilete with radially symmetrical exine sculpture comprising three sets of parallel or near‐parallel muri. Anemia has six spore types. One is reticulate (A. wrightii‐type), and the other five types have either cicatricose or canaliculate sculpture that reflect a basic form, i.e., three mural sets that have mutual anastomoses in each radial region. The cicatricose A. mexicana‐ and the canaliculate A. dregeana‐types represent the simplest expressions of this pattern. Specializations include cicatricose, auriculate (A. raddiana‐type) and canaliculate, ornate (A. oblongifolia‐, A. phyllitidis‐types). Exine structure is homogeneous or differentially microporate; the enveloping two‐layered perine has granulate structure and a granulate to spiculate and/or pitted surface. Mohria spores have a stratified, granulate to rugulose perine and cicatricose exine sculpturing consistent with the A. mexicana‐type pattern, but the muri are hollow. The canaliculate spores of Ceratopteris differ from those of Anemia and Mohria in that the three mural sets are discrete and separated from each other by a stria in each radial region; exine structure is homogeneous and the thin perine is granulate. Within Anemia the A. raddiana‐type is exclusive to subgen. Coptophyllum and the A. oblongifolia‐ and A. phyllitidis‐types to subgen. Anemia. Three spore types are shared by two subgenera; i.e., A. wrightii‐ and A. mexicana‐types in Coptophyllum and Anemirhiza, and the A. dregeana‐type in Anemirhiza and Anemia. Spore polymorphism is indicated in several species of subgen. Anemia, and smooth immature spores are recorded from all three subgenera.
REPRODUCTIVE STRATEGY OF CLEISTES DIVARICATA (ORCHID ACEAE)
Authors: Gregg Katharine B.
Published: January 2018

In Cleistes divaricata, a hinged anther dispenses a sequence of loosely aggregated pollen tetrad masses onto the dorsal thorax of Bombus and Megachile workers. This mechanism allows more than one bee to receive pollen from a single flower. To determine the effectiveness of this strategy, plants in bud were caged and hand pollinated using pollen from sequential releases. Capsules produced from a flower's first three pollen dumps were significantly larger and heavier and contained more seeds than those produced by later pollen deposits with fewer tetrads. Decreasing pollen dosage did not affect fruit set, capsule development, individual seed weight, or percentage of healthy looking embryos per fruit. Fruit set for artificial pollinations was 93% for pollen dumps 1–3 and 97% for dumps 4–18. As set of naturally pollinated marked plants was only 38%, low frequency of pollinator visits apparently limited seed production. Efficacy of infrequent visits is maximized, however, because a flower's first pollen releases contain the most pollen, but later low‐dosage dumps can produce some seeds. An unexpected cost was a higher investment of pericarp per seed in low‐dosage capsules (130 ng pericarp seed‐1 fresh weight) than in high‐dosage pollinations (only 27 ng pericarp seed–1). Flower fading in plants receiving low pollen dosage was as slow as that in caged, unpollinated controls, thus increasing opportunity for additional pollination.
LABILE SEX EXPRESSION IN ANDROMONOECIOUS SOLANUM HIRTUM: FLORAL DEVELOPMENT AND SEX DETERMINATION
Authors: Diggle Pamela K.
Published: January 2018

Sex expression (the proportions of hermaphrodite and staminate flowers produced) of the andromonoecious species Solatium hirtum is labile, and this lability of whole plant sex expression is due to labile sex expression of individual floral buds. In this paper I examine the developmental processes that underlie the differences in floral sex expression of hermaphrodite and staminate flowers of Solarium hirtum, focusing particularly on the processes responsible for the observed lability of floral sex expression. Differences in bud growth rate and relative growth of floral organs in these buds are evident at about the time of megasporocyte meiosis (11–12 days before anthesis). However, gynoecial sterility in staminate buds does not occur until just 6–7 days before anthesis. At this time, abnormalities in ovule development occur in staminate buds: the ovules begin to appear necrotic, the integumentary tapetum collapses, and the megagametophytes of many ovules cease normal development. These observations are consistent with the predictions of labile floral development.
DIFFERENTIAL RNA SYNTHESIS IN THE SHOOT APEX OF PHARBITIS NIL DURING FLORAL EVOCATION
Authors: Bonner Bruce A. , Gifford Ernest M. , Reed Nu‐May Ruby
Published: January 2018

Early events in the evocation of the flower in Pharbitis nil Chois seedlings were investigated by following the incorporation of tritiated uridine into the shoot apex. The uridine was applied to the expanded cotyledons of seedlings at 8 hr into the inductive dark period. The shoot tips were fixed at 20 hr (a 12‐hr labeling period). After the 12‐hr labeling period there was considerable label throughout the shoot tips of both control plants (dark period interrupted with 5 min of red light at 8 hr) and plants induced to flower. Both RNase and acid hydrolysis removed the nonexchangeable label and the Azure B staining, thus leading to the conclusion that the uridine was incorporated into RNA. Induction in the cotyledons was followed quickly by an increased synthesis of RNA in the rib meristem region of the receptor bud at the time when the floral stimulus is assumed to be arriving. The increase in RNA synthesis is revealed by an increase in the rib meristem/central zone ratio of counts due to the incorporation of tritiated uridine. A comparison of counts in each of the two regions revealed that the change in ratio was due to an increase in the rib meristem and not due to a decrease in the central zone in induced shoot apices. The initial activation of the rib meristem probably occurred by 16 hr from the beginning of the dark period. Tendencies in the literature to disregard the role of the rib meristem in giving rise to part of the flower are discussed.
THE EFFECT OF GENETICALLY BASED DIFFERENCES IN SEED SIZE ON SEEDLING SURVIVAL IN ARABIDOPSIS THALIANA (BRASSICACEAE)
Authors: Krannitz Pam G. , Aarssen Lonnie W. , Dow Jennifer M.
Published: January 2018

The relationship between genetically different seed sizes and seedling survival under severe nutrient deprivation was determined by comparing ten inbred lines of Arabidopsis thaliana. Seedlings were supplied with only sterile distilled water, and the number of days between germination and death (complete chlorosis) was recorded. Seedlings from genotypes with larger seeds survived longer than seedlings from genotypes with smaller seeds. These results suggest a genetically based adaptive significance of larger seed size resulting from a greater seedling tolerance of nutrient deprivation. This may confer a potentially important selective advantage when nutrient deprivation is the result of a low resource supply in the environment, or the result of nutrient depletion by neighbors.