bluuebunny/crossref_metadata_2025 huggingface dataset:
MATING SYSTEM AND DISTRIBUTION OF GENETIC VARIATION IN GYMNOCARPIUM DRYOPTERIS SSP. DISJUNCTUM
Authors: Kirkpatrick Ruth E. B. , Soltis Pamela S. , Soltis Douglas E.
Published: January 2018

Levels and distribution of genetic variation were analyzed in 15 populations of the homosporous fern Gymnocarpium dryopteris ssp. disjunctum to evaluate the mating system and the genetic structure of this taxon. Estimated rates of intragametophytic selling were 0.000 in all populations, signifying that all sporophytes examined arose via intergametophytic matings. Furthermore, values of F, the fixation index, ranged from –0.171 to 0.038, indicating that all populations approach Hardy‐Weinberg equilibrium. Therefore, not only is intragametophytic selling rare in G. dryopteris ssp. disjunctum, but intergametophytic selling is also uncommon. Factors promoting outcrossing in G. dryopteris ssp. disjunctum include an antheridiogen system, an ontogenetic sequence that favors intergametophytic matings, and high levels of genetic load. Analysis of F‐statistics indicated statistically significant genetic differentiation among populations despite a mean genetic identity of 0.973 and high levels of interpopulational gene flow (Nm = 3.41 to 4.09). These patterns may reflect levels of gene flow that prevent significant interpopulational divergence while permitting slight genetic differentiation among populations.
STIGMA OF SOLANUM TUBEROSUM CV SHEPODY: MORPHOLOGY, ULTRASTRUCTURE,AND SECRETION
Authors: Mackenzie Cynthia J , Yoo Bong Y. , Seabrook Janet E. A.
Published: January 2018

The stigma of Solarium tuberosum L. cv Shepody has a bilobed papillate surface covered with a viscous secretion at anthesis. The secretion originates as osmiophilic droplets in the cytoplasm, accumulates in the intercellular space, and fills the base of the papillae, after lifting and rupturing the cuticular layer covering the stigma surface. Cytochemical evidence shows that the stigmatic secretion is lipidic in nature; it did not stain with the periodic acid‐Schiffs reaction for carbohydrate or Coomassie Brilliant Blue R‐250 for proteins, but did stain with Sudan black or Nile red, a fluorescence probe for lipids. Sodium dodecylsulfate‐polyacrylamide gel electrophoresis has revealed that the secretion contained three polypeptides that appeared to be 'indigenous' to the stigmatic secretion, and not contaminants. Comparative analyses of this and other proteins found in stigma secretions may provide clues to their possible roles in pollen grain adhesion and germination.
PHENOTYPIC GENDER IN SEX CHANGING DWARF GINSENG, PANAX TRIFOLIUM (ARALIACEAE)
Authors: Schlessman Mark A.
Published: January 2018

Dwarf ginseng (Panax trifolium L., Araliaceae) is a diphasic (“sex changing”) species in which one phase has staminate flowers and the other has hermaphroditic flowers. In order to determine the relative allocations of the hermaphroditic gender phase to male and female functions,variation in population gender phase ratios, pollen production and viability, and ovule and seed production were documented. Gender phase ratios are highly male‐biased. Dwarf ginseng is self‐compatible, and both gender phases have viable pollen capable of effecting fertilization. Males produce more flowers and more viable pollen per anther than hermaphrodites. The phenotypic gender of hermaphrodites is extremely female‐biased; it is likely that hermaphrodites function essentially as females. Sexual selection may have a role in the evolution and maintenance of differences between the gender phases in allocation to male function.
SIEVE TUBES IN FOLIAR VEIN ENDINGS: REVIEW AND QUANTITATIVE SURVEY OF RUDBECKIA LACINIATA (ASTERACEAE)
Authors: Lersten Nels R.
Published: January 2018

Sieve tube distribution in foliar vein endings of angiosperms is mentioned in 33 publications. Their collective judgment is that sieve tubes may be lacking, may end partway along, or may extend to the vein tip. Most reports conclude that all vein endings are the same within a species, but a few studies mention variation. Only three studies include quantitative data, all based on reconstruction from microtome sections. The present quantitative study, the most extensive one to date, surveyed sieve tubes in vein endings from cleared and stained leaf pieces of Rudbeckia laciniata (Asteraceae, tribe Heliantheae), a North American perennial herb. Of 203 areoles sampled, 32 (15.8%) lacked vein endings whereas 171 (84.2%) had one to six endings per areole. There were 385 individual vein endings in the 171 areoles: 115 lacked sieve tubes, 38 had them to the vein tip, but in most (232) they ended at some intermediate point. Serial cross sections of the latter showed phloem parenchyma continuing beyond the sieve tubes for some distance, beyond which occurred a distal zone consisting solely of tracheary elements. R. laciniata vein endings exhibit the same range of variation reported for dicots in general. More studies combining clearings with selected sections are needed to establish the range of vein ending patterns among angiosperms.
SUBTERRANEAN SPOROPHYTIC GEMMAE IN MOONWORT FERNS, BOTRYCHIUM SUBGENUS BOTRYCHIUM
Authors: Farrar Donald R. , Johnson‐Groh Cindy L.
Published: January 2018

Underground gemmae in Botrychium subgenus Botrychium are described as the first report of such structures in ferns. Gemmae are spherical units 0.5–1 mm in diameter produced on the stem, where they originate in meristematic regions of the outer cortex. At maturity they contain an embedded apical cell and may contain a mycorrhizal fungus. Upon abscission from the stem they remain subterranean and may undergo growth and development into completely differentiated sporophytes in a pattern similar to that of development of sexually produced embryos. In addition to the diploid B. campestre, gemmae occur in the tetraploids B. minganense, B. echo, and a new species as yet undescribed. These may be allotetraploids of which B. campestre is one parent. The ecological significance of reproduction by gemmae may lie in the advantages of asexual reproduction in the dry prairie habitat of B. campestre.
MYCORRHIZAE IN RECENT VOLCANIC SUBSTRATES IN HAWAII
Authors: Gemma J. N. , Koske R. E.
Published: January 2018

Plants colonizing 8‐ and 14‐year‐old lava flows, a 28‐year‐old cinder fall, a 137‐year‐old volcanic soil, and a geothermic volcanic soil were sampled for mycorrhizae. Vesicular arbuscular mycorrhizae were present in all sites, and the frequency of occurrence and intensity of root colonization increased with increasing age of the site. In the youngest site, 57% of the sampled species were mycorrhizal, and this increased to 84% in the cinder fall and 100% in the old soil. Orchid and ericoid mycorrhizae also were present in some sites. Native Hawaiian species tended to more frequently form mycorrhizae and have more intense mycorrhizal infection than did alien species. Plant succession on the Hawaiian volcanic sites differed somewhat from a predictive model in the lack of dominance by nonmycotrophic species in the early seral stages. The difference apparently results from 1) the arrival of mycorrhizal fungi soon after the volcanic substrates cool and 2) the paucity of nonmycotrophic species available to invade very recent volcanic sites.
LOCAL GENETIC AND CLONAL STRUCTURE IN THE TROPICAL TERRESTRIAL BROMELIAD, AECHMEA MAGDALENAE
Authors: Murawski Darlyne A. , Hamrick J. L.
Published: January 2018

The genetic structure of populations of the clone‐forming tropical terrestrial bromeliad, Aechmea magdalenae, was examined by electrophoretic analyses in nine populations occurring on and near Barro Colorado Island, Republic of Panama. For the nine populations as a whole, 33% of the loci were polymorphic and the genetic diversity was 0.121. Within populations, the mean percent of polymorphic loci was 24.1% and the mean genetic diversity was 0.084. About one‐third of the total allozyme diversity resided among populations (mean GST = 0.356). The distribution of A. magdalenae was patchy in the study area. This, coupled with the relatively small effective population sizes and the possible founding of populations by few individuals may have contributed to the large among‐population component of genetic diversity. The extent of clonal growth was inferred by examining the relationship between the proportion of rosette‐pairs sharing identical multilocus genotypes and distance between pairs. This method indicates that clonal spread is local; individuals sharing multilocus genotypes most often occur within 10 m of each other.
CONE AND OVULE ONTOGENY IN TAXODIUM AND GLYPTOSTROBUS (TAXODIACEAE – CONIFERALES)
Authors: Takaso T. , Tomlinson P. B.
Published: January 2018

Seed cones in Taxodium distichum and Glyptostrobus pensilis occupy the position of permanent shoots and are initiated in the summer preceding spring pollination. Morphological features are similar in the two genera, reflecting their close taxonomic relationship. Ovule complexes originate as two (rarely more) ovule primordia in the axil of each fertile bract but without any indication of a preceding discrete ovuliferous scale. When the nucellus, integument, and micropyle are well developed, a series of up to ll abaxial lobes forms at the base of each ovule pair. They become fused by basal growth. After pollination the common basal meristem of lobes and bract extends by intercalary growth to form the conspicuous “ovuliferous scale” of the mature cone; the lobes enlarge and exceed the ovules. Despite the topographic similarity in the cones of both genera, there are differences in vasculature such that the vascular traces to the axillary complex originate directly from the axial cylinder in Glyptostrobus but from the bract trace in Taxodium. The complex vasculature of the mature cone develops late and primarily as an expression of intercalary growth.
MATERNAL EFFECTS AT FOUR LEVELS IN SENECIO VULGARIS (ASTERACEAE) GROWN ON A SOIL NUTRIENT GRADIENT
Authors: Aarssen L. W. , Burton S. M.
Published: January 2018

Plants of Senecio vulgaris L. were grown individually within pots to examine effects of maternal soil nutrient level on offspring. Genotypic variability among maternal plants was minimized by using only maternal plants derived from seed of a single inbred line. Significant (P < 0.05) maternal effects of the nutrient gradient were detected at four different levels. Maternal plants grown in lower soil nutrients produced: 1) seeds with lower individual mass; 2) seeds that germinated later; 3) seedling offspring that grew into smaller juvenile plants in nutrient‐impoverished soil; and 4) seedling offspring that survived longer in the absence of external nutrients. This last type of maternal effect is reported for the first time in the present study. These data suggest that a compensatory effect of relatively low maternal soil nutrient level may be conferred on the plant's offspring in the form of a “wait and tolerate” strategy through a longer “seedling dormancy” period. This appears to involve a high seedling tolerance threshold level for external nutrient deprivation. To account for these results, we propose two hypotheses based on two different causes of nutrient deprivation, and based on the assumption that if maternal plants experience nutrient deprivation, seedling offspring have a high probability of also experiencing the same cause of nutrient deprivation: 1) Under the “nutrient supply hypothesis,” the wait and tolerate strategy in seedling offspring represents an adaptation to selection factors associated with nutrient deprivation resulting from a low nutrient‐supplying power of the environment. 2) Under the “nutrient‐depletion hypothesis,” this strategy represents an adaptation to selection factors associated with nutrient depletion by neighbors.
SEX‐RATIO AND REPRODUCTIVE VARIATION IN THE MISTLETOE PHORADENDRON JUNIPERINUM (VISCACEAE)
Authors: Dawson Todd E. , Ehleringer James R. , Marshall John D.
Published: January 2018

Despite the fact that many parasitic and hemiparasitic plant species such as mistletoes are dioecious and occur in both the new and the old world, few data exist on variation in the sex ratio and allocation to reproduction in these taxa. We investigated 1) the sex‐ratio of the xylem‐tapping mistletoe Phoradendron juniperinum in relation to its age and position within the canopy of its host tree Juniperus osteosperma, and 2) reproductive effort in relation to the gender and age of mistletoe plants. Our surveys showed that P. juniperinum has a male‐biased sex ratio. Despite this predominance of male individuals, females lived longer and had a greater reproductive effort than did males. A statistical analysis of the age distribution data indicated that the peak in the frequency of reproductively mature individuals was later in females than in males. These gender‐specific distributions may have resulted 1) from sequential hermaphroditism (age‐specific sex switching), or 2) because the average age of peak reproduction is later in female individuals. Because sex is genetically determined in a closely related genus of mistletoe and because we have no data to indicate sex switching in this species, we feel that our data support the interpretation that female individuals, on average, show a peak in reproductive vigor at an older age relative to males. While delayed reproduction in females may be favored because reproductive effort and success appear to be age‐dependent in females of this species, both sexes can become reproductively mature relatively early in life. Further, because 1) allocation to reproduction as a function of age increases more rapidly for females of this species relative to males, and 2) because there may be a higher resource cost associated with reproduction in females, we hypothesized that female individuals would be more abundant in the best quality locations within the host tree so as to maximize the opportunity to meet those costs. In spite of the association between gender and some host characteristics, there was no indication that female plants were located in sites most favorable to either their carbon or water balance. We discuss reasons why this may be the case.
ULTRASTRUCTURE OF ARRESTED EMBRYOS FROM LETHAL MUTANTS OF ARABIDOPSIS THALIANA
Authors: Patton David A. , Meinke David W.
Published: January 2018

The purpose of this study was to examine the extent of cellular differentiation in arrested embryos from lethal mutants of Arabidopsis thaliana. The question to be addressed was whether arrested embryos in heterozygous siliques resembled mature wild‐type embryos at the cellular level. Protein bodies were chosen as developmental markers because they appear only during the final stages of embryogenesis. Both the hypocotyl and cotyledons of wild‐type embryos contained protein bodies that became filled with storage protein during the cotyledonary stages of development. Some mutant embryos (emb30) contained normal protein bodies and resembled mature wild‐type embryos at the cellular level. Other mutant embryos (emb22) contained only immature protein bodies and were therefore blocked in both morphogenesis and cellular differentiation. The formation of protein bodies in emb31 was normal in the hypocotyl but delayed in the cotyledons. In this case the mutant gene appears to disrupt the timing of both morphogenesis and differentiation. This ultrastructural view of arrested embryos has provided additional information on the nature of developmental arrest that should facilitate the classification of embryonic lethals and the identification of mutants with defects in developmental rather than housekeeping functions.
ALLELOPATHIC AND HERBICIDAL EFFECTS OF EXTRACTS FROM TREE OF HEAVEN (AILANTHUS ALTISSIMA)
Authors: Heisey Rod M.
Published: January 2018

Mature trees of Ailanthus altissima produce one or more potent inhibitors of seed germination and seedling growth. Inhibitor activity is highest in bark, especially of roots, intermediate in leaflets, and low in wood. Crude extracts of Ailanthus root bark and leaflets corresponding to 34 and 119 mg water extractable material/L, respectively, caused 50% inhibition of cress radicle growth. Ailanthus seeds also contain one or more inhibitors. These are bound within the seed by the pericarp but diffuse into water agar when the pericarp is removed. The inhibitor(s) could readily be extracted from Ailanthus tissues with methanol, but not dichloromethane, indicating polar characteristics. Ailanthus leaflets had highest inhibitory activity during expansion in spring, whereas activity of trunk bark peaked just before emergence of leaves. This pattern suggests transport of allelochemicals from bark into new leaves. A comparison of seven plant species for sensitivity to the inhibitor(s) from Ailanthus root bark showed little selectivity, although velvetleaf was somewhat more resistant. The inhibitor(s) from Ailanthus root bark exhibited strong herbicidal effects when sprayed pre‐ and postemergence on plants in soil in the greenhouse. Postemergence effects were striking, with nearly complete mortality of all species, except velvetleaf, at even the lowest doses tested. The results suggest the allelochemical(s) from Ailanthus may have potential for development as natural‐product herbicides.
AMONG‐ AND WITHIN‐FLOWER COMPARISONS OF POLLEN TUBE GROWTH FOLLOWING SELF‐ AND CROSS‐POLLINATIONS IN DIANTHUS CHINENSIS (CARYOPHYLLACEAE)
Authors: Aizen Marcelo A. , Searcy Karen B. , Mulcahy David L.
Published: January 2018

We compared the rate of pollen tube growth following self‐ and cross‐pollinations both among and within flowers of two clones of Dianthus chinensis L. For among‐flower comparisons, both styles of a flower were pollinated with either self‐ or cross‐pollen. Within‐flower comparisons were made between the two styles of the same flower, one of which was self‐pollinated and the other cross‐pollinated. Comparisons between flowers indicated that self‐pollen grew slower than cross‐pollen in both clones. However, differences in the growth rate of pollen tubes from self‐ and cross‐pollinations were greater when comparisons were made between the two styles of the same flower than when pollinations were made in different flowers. These results suggest the existence of interstyle interactions in pollen tube growth.
GENETIC STRUCTURE OF THE AUSTRALIAN CYCAD, MACROZAMIA COMMUNIS (ZAMIACEAE)
Authors: Ellstrand Norman C. , Ornduff Robert , Clegg Janet M.
Published: January 2018

Cycads have been the subject of a wide variety of botanical studies. However, nothing is known of the genetic structure of their populations. Seeds were collected from five populations of the common Australian cycad Macrozamia communis along a north to south transect through its 500‐km‐long range in eastern New South Wales. Leaf samples from seedlings grown from those seeds were the subject of isozyme analysis. Nine of the 18 isozyme loci studied were polymorphic. Levels of polymorphism varied among loci and among populations. The three southern‐most populations were genetically similar to one another but well differentiated from the other two. The levels of species‐wide genetic diversity observed for M. communis were relatively low compared with those of other gymnosperms and angiosperms. On the other hand, the levels of spatial differentiation were relatively high, especially compared with other gymnosperms.
CARBON UPTAKE CHARACTERISTICS IN TWO HIGH ELEVATION POPULATIONS OF THE AQUATIC CAM PLANT ISOETES BOLANDERI (ISOETACAE)
Authors: Sandquist Darren R. , Keeley Jon E.
Published: January 2018

In the aquatic CAM species Isoetes bolanderi, a resident of high elevation lakes in which ambient carbon levels are low and fairly constant throughout the day, CO2 uptake by the leaves generally parallels changes in photosynthetic photon flux density as opposed to changes in ambient CO2 levels. Overnight CO2 uptake by the leaves of I. bolanderi contributed up to 33% of the total daily carbon assimilation from the water column which is typical of aquatic CAM species but low in comparison to the 30–50% seen in the seasonal pool congener Isoetes howellii. Two additional sources of carbon may supplement the 24‐hour period for carbon assimilation conferred by CAM in I. bolanderi: the refixation of respiratory CO2 and carbon acquisition from the interstitial sediment water via roots. CAM appears to play a significant role in enhancing carbon gain in I. bolanderi which dominates the littoral flora of Siesta and Ellery Lakes despite higher carbon uptake rates from the water column found in one associated macrophyte Fontinalis antipyretica.
TRIPSACUM ANDERSONII IS A NATURAL HYBRID INVOLVING ZEA AND TRIPSACUM: MOLECULAR EVIDENCE
Authors: Talbert Luther E. , Doebley John F. , Larson Steven , Chandler Vicki L.
Published: January 2018

Cytogenetic evidence suggests that Tripsacum andersonii may be a natural hybrid between Zea and Tripsacum. In this paper we show sequences that hybridize to the transposable elements Mul and Spm are found in T. andersonii and all Zea species examined. However, no hybridizable sequences are observed in the five other Tripsacum species surveyed. These results suggest that Mu and Spm elements became components of the Zea genome after the divergence of Zea and Tripsacum, and they strongly support the cytological evidence that T. andersonii is a Zea‐Tripsacum hybrid. Examination of nuclear ribosomal genes of T. andersonii also supports the hybridization hypothesis and identifies the Zea parent as Zea luxurians. The Tripsacum parent could not be conclusively identified, but the ribosomal gene data suggest that the species of Tripsacum section Fasiculata most closely resemble T. andersonii. Restriction site patterns of two chloroplast DNA sequences indicate that the maternal parent was a species of Tripsacum. These results are complemented by morphological evidence regarding the origin of T. andersonii.
DETERMINATE GROWTH OF ALLIUM SATIVUM PEDUNCLES: EVIDENCE OF DETERMINATE GROWTH AS A DESIGN FACTOR FOR BIOMECHANICAL SAFETY
Authors: Niklas Karl J.
Published: January 2018

Determinate growth in an organ can reduce the mechanical liability of dynamic wind loadings. This hypothesis was examined for the peduncles of Allium sativum grown under protected and unprotected field conditions and in the glasshouse. The extent to which the lengths of peduncles approach their critical buckling lengths lcr was correlated with the extent to which peduncles were perturbed mechanically. Glasshouse‐grown plants that were protected from dynamic loadings (wind or handling) produced peduncles with low ratios of critical to actual peduncle lengths (lcr/1 = 1.11 ± 0.07); field‐grown, unprotected plants had lcr/1 = 1.85 ± 0.29; while plants grown in the field but protected from the wind had lcr/1 = 1.29 ± 0.15. Statistical analyses indicated that peduncle length was the only morphometric parameter examined to significantly differ among plants grown under the three conditions. The frequency distributions of critical (buckling) stress for each of the three populations of peduncles differed; that of the unprotected population conformed to a three‐parameter Weibull distribution. Allium sativum exhibits thigmomorphogenesis, i.e., mechanical forces influence the extent and nature of organogenesis. Unlike other thigmomophogenetic species, however, the determinate growth of peduncles did not influence peduncle girth or the elastic (Young's) modulus of tissues. Thus, the extent to which vertical growth proceeded determined the design factor for dynamic loading in these reproductive organs. The design (“margin of safety”) factors of A. sativum peduncles grown under the three different conditions and calculated from lcr/1 were remarkably similar to those specified for engineered columns of wood subjected to stress durations differing in magnitude.
CHLOROPLAST DNA POLYMORPHISM AND PHYLOGENY IN THE B GENOME OF GLYCINE SUBGENUS GLYCINE (LEGUMINOSAE)
Authors: Doyle Jeff J. , Doyle Jane L. , Brown A. H. D.
Published: January 2018

The B genome of Glycine subgenus Glycine comprises three diploid species whose monophyly is supported by morphological, crossing, and chloroplast DNA (cpDNA) data. Previous cpDNA studies indicated low levels of divergence among these taxa and failed to resolve cladistic relationships among them. More intensive studies of cpDNA variation were initiated, using additional restriction endonucleases and accessions. Results from cladistic analyses of over 50 restriction site characters indicate that there is considerable cpDNA polymorphism within this group of species, with a minimum of 27 plastome types occurring among the 74 accessions sampled. Levels of homoplasy observed in this group are relatively high (15%) for closely related congeneric species. There is only limited congruence between plastome type and taxonomic classification based on morphological characters. Explanations for this lack of concordance include: 1) the early state of taxonomic understanding in this group, 2) lack of resolution in the cpDNA tree caused by homoplasy and the small number of synapomorphic characters, 3) introgression among these interfertile, often sympatric taxa, and 4) maintenance of ancestral cpDNA polymorphisms resulting in shared plastomes among species.
GENETIC DIFFERENTIATION AND HYBRIDIZATION BETWEEN CAREX GYNODYNAMA AND C. MENDOCINENSIS (CYPERACEAE) IN CALIFORNIA
Authors: Waterway Marcia J.
Published: January 2018

Patterns of variation within and between Carex gynodynama and C. mendocinensis were investigated by studying allozyme and chromosome variation in natural populations and structural variation using herbarium specimens. Multivariate analyses of structural data demonstrated that C. gynodynama is clearly distinct from C. mendocinensis, and that sterile specimens similar to C. mendocinensis are intermediate between that species and C. gynodynama. The mean genetic distance between the two species, based on allozyme phenotypes at 17 enzyme‐coding loci, was 0.22 ± 0.12. The sterile putative hybrids had the expected heterozygous pattern at three enzyme‐coding loci at which the parental species were fixed for different alleles. Chromosome numbers are reported for the first time for both species and their putative hybrid. Carex mendocinensis had a different number in each of the three populations examined with n = 28, n = 29, or n = 30. Chromosome counts from one population of C. gynodynama revealed five plants with n = 25 and one with n = 26. Putative hybrids from this population exhibited irregular pairing at meiosis with 2n = ca. 55–57. Patterns of allozyme variation also suggest that C. mendocinensis has an outcrossing or mixed mating system but that C. gynodynama is an inbreeding species. Carex gynodynama exhibited very little variation in structure, habitat, or at the enzyme‐coding loci examined, suggesting that it may have experienced a genetic bottleneck relatively recently. Carex mendocinensis had higher levels of variation both within and between populations at enzyme‐coding loci and in structural features. This pattern of variation and a geographic distribution centered in serpentine areas of the Klamath–Siskiyou region, with disjunct smaller populations in serpentine areas farther south, suggest that C. mendocinensis once may have been a more widespread species.
AN OVERVIEW OF THE GENUS PYRRHOPAPPUS (ASTERACEAE: LACTUCEAE) WITH EMPHASIS ON CHLOROPLAST DNA RESTRICTION SITE DATA
Authors: Turner B. L. , Kim Ki‐Joong
Published: January 2018

The genus Pyrrhopappus in recent systematic treatments has comprised five taxa (four species, one with two varieties), which have now been studied anew using morphogeographical and chloroplast DNA restriction site data. Eight populations, representing all of the recognized taxa of Pyrrhopappus, were digested with 17 restriction enzymes. Only three restriction site differences were found from among 750 restriction sites and no length variations were observed. This contrasts with similar studies, using these same enzymes, on the closely related genus Krigia in which 173 mutation sites and 20 length variations were found among the seven species concerned. Nucleotide sequence divergence values among the species of Pyrrhopappus were extremely low (0.0012) compared to much higher values found in the closely related genus Krigia (0.1270). Three species of Pyrrhopappus are herein recognized: two diploids with 2n = 12 chromosomes, P. carolinianus and P. pauciflorus (including P. multicaulis, P. geiseri and P. rothrockii), and a tetraploid (2n = 24), P. grandiflorus. The tetraploid is partially sympatric with both diploids but is readily recognized by its perennial roots, which bear tuber‐like enlargements. These three species presumably arose relatively recently, and the DNA data suggest that neither P. pauciflorus nor P. carolinianus gave rise to the tetraploid P. grandiflorus.
AUTORADIOGRAPHIC STUDY OF RNA SYNTHESIS DURING SECONDARY RHIZOID CELL DIFFERENTIATION IN PTERIS VITTATA
Authors: Cohen David , Crotty William J.
Published: January 2018

The pre‐ and postmitotic stages of rhizoid cell differentiation in Pteris vittata L. were pulsed in radioactive uridine for 30 min and the data analyzed quantitatively by autoradiography. The total grain count rises from 594 in the nondifferentiating cell to 1,369 in the corona stage; increases to 2,745 in the internally segmented rhizoid cell (IRC) and to 2,779 in the wheel; and then drops to 1,306 in the protrusion and to 1,261 in the early rhizoid. The significant increase in nucleolar labeling in the corona reflects an increase in ribosomal RNA synthesis for mitosis‐associated syntheses. The two‐fold increase in grains over the cellular compartments of the IRC and wheel reflects an increase in RNA synthesis in these postmitotic stages. The similarity of labeling profiles between these stages suggests that they are not far enough separated to show a difference in their roles. The decline in total grain counts in the protrusion and early rhizoid stages to half the maximum levels suggests that an overall decrease in RNA synthesis is attended by a shift from a differentiating phase to a steady‐state growth system.
INTERFERENCE THROUGH IMPROPER POLLEN TRANSFER IN MIXED STANDS OF IMPATIENS CAPENSIS AND I. PALLIDA (BALSAMINACEAE)
Authors: Randall John L. , Hilu Khidir W.
Published: January 2018

Mechanisms of interference through improper pollen transfer are described for sympatric populations of the simultaneously flowering annuals Impatiens capensis and I. pallida. Stigmas of both Impatiens species are receptive to conspecific pollen from the time of androecium disarticulation until after perianth drop. Pollen of I. pallida adheres to, and germinates on, the stigmas of I. capensis. The pollen tubes reach the ovules but do not fertilize them. In contrast, pollen of I. capensis adheres poorly to I. pallida stigmas and fails to germinate. Pollen mixtures of the two Impatiens species cause a much greater reduction in fruit set in I. capensis than in I. pallida. Despite the interference of I. pallida pollen, I. capensis persists in mixed populations with I. pallida by: 1) possessing stigmas receptive to pollen throughout the female phase; 2) having the ability to produce a full seed complement via one pollination event; and 3) possessing cleistogamous flowers to ensure sexual reproduction.
ENVIRONMENTAL CONTROL OF SEED GERMINATION IN THLASPI ARVENSE (CRUCIFERAE)
Authors: Hazebroek Jan P. , Metzger James D.
Published: January 2018

The effect of environmental conditions during storage and imbibition on germination was investigated in field pennycress (Thlaspi arvense L.), a weed species that can behave as a winter or a summer annual. Freshly harvested seeds of an inbred line with a cold requirement for flowering exhibited primary dormancy that was rapidly lost following 1 month of afterripening in a dry state. Nondormant seeds were positively photoblastic. The light effect was mediated through phytochrome since germination was promoted by red light and inhibited by far red light. Seedling emergence was also inhibited by light filtered through a canopy of wheat leaves. Germination of field pennycress seeds was considerably more sensitive to moisture stress than two sympatric species, wild oat (Avena fatua L.) and wheat (Triticum aestivum L., cv. ERA). Seeds of the latter two species were chosen in order to compare the effect of water potential on germination in field pennycress with that in sympatric species. It was concluded that the major environmental factor limiting nondormant field pennycress seeds on the soil surface was water availability. Imbibition of fully afterripened seeds at low temperatures (6 C) induced a deep secondary dormancy. In contrast to primary dormancy, cold‐induced dormancy was not alleviated by red light, alternating temperatures (21/5 C), or 2 months of dry storage at 6, 15, or 35 C. However, exogenous gibberellin A3 or 24 weeks of dry storage resulted in germination in cold‐induced dormant seeds. Secondary dormancy was not observed in fully afterripened seeds that were preincubated at 21 C for 1 or 2 days prior to the cold treatment. These results may explain the failure in field experiments to observe the cold‐induced secondary dormancy that limits spring emergence in other winter annuals (J. Baskin, C. Baskin, Weed Res. 1979 19: 285–292).
SEASONAL PATTERN OF SEEDLING EMERGENCE, SURVIVAL, AND REPRODUCTIVE BEHAVIOR IN THLASPI ARVENSE (CRUCIFERAE)
Authors: Hazebroek Jan P. , Metzger James D.
Published: January 2018

The timing of seedling emergence, survival, and reproductive development (bolting and flowering) of field pennycress (Thlaspi arvense L.) in outdoor plots was investigated for two inbred lines with different vernalization requirements. Seeds of a cold‐requiring line sown in early September germinated by the end of the month or during the following spring. Seedling emergence from seeds sown in late September and October was observed only in the spring and fall of the following year. Reproductive development in plants that emerged in the fall occurred during the following spring and was earlier than spring‐emerging plants. Seedlings from spring‐sown seeds emerged on dates that coincided with periods of cool wet weather. Few seedlings emerged during the summer, and those that did had low survival. Plants from spring‐sown seeds of the cold‐requiring line and a non‐cold‐requiring line exhibited similar time courses for reproductive development, indicating negligible ecological significance for the differences in vernalization requirements of the two lines.

The time of the year when the vernalization requirements are met for the cold‐requiring field pennycress line was investigated by transplant studies. Plants transplanted outdoors in the fall flowered the following spring. Depending on the date the plants were moved outdoors, vernalization was complete in spring transplants as well. For plants placed outdoors in early fall or in early spring and then returned at monthly intervals to constant 21 C, the duration of vernalizing temperatures strongly influenced the rate of reproductive development (rate of stem growth, final stem height, and time for open flowers to appear). Maximum vernalization was achieved after 3 and 2 months outdoors in the fall and spring transplantings, respectively. The quantitative relationship between the rate reproductive development and the duration of vernalizing temperatures was the same for spring and fall transplants. Thus, timing of emergence of field pennycress seedlings coincides with periods of maximum vernalization potential with the net result being that despite the cold requirement for seed production in some ecotypes, this species behaves as both a winter and summer annual.
STEMS AND LEAVES OF CUNNINGHAMIOSTROBUS GOEDERTII FROM THE OLIGOCENE OF WASHINGTON
Authors: Miller Charles N.
Published: January 2018

This report is based on nine specimens of fossil conifer stems and leaves from the Early Oligocene Jansen Creek Member of the Makah Formation. They were collected along the northern shore of the Olympic Peninsula of Washington. The fossils are preserved as siliceous permineralizations and were exposed in surface view along rock fractures. Details of leaf morphology and epidermal construction appear on fracture surfaces of certain specimens while the cellular construction of the leaves and twigs is visible in thin sections. Leaves are dorsiventrally flattened, attached to twigs that contain up to four growth increments of secondary xylem, up to 2.3 cm long, 3.5 mm wide, and have parallel margins with minute teeth. The leaves are about 0.5 mm thick and have a central vascular strand surrounded by transfusion tissue. A large resin canal occurs abaxial to the vascular strand, and generally two additional resin canals occur in the mesophyll near each leaf margin. Leaves are mostly hypostomatic, with sunken stomata in two longitudinal bands, one to each side of the midline of the leaf and each containing eight to 13 longitudinal rows of stomata. Several unusual anatomical features in the stems also occur in the peduncle and cone axis of seed cones described as Cunninghamiostrobus goedertii, which occurs at the same locality. Thus, the leafy twigs belong to the same species as produced the cones. The cones, leaves, and shoots of this Tertiary conifer are similar to those of modern Cunninghamia but differ from the living species in several respects.
ULTRASTRUCTURAL STUDY ON MICROSPORE WALL MORPHOGENESIS IN ISOETES JAPONICA (ISOETACEAE)
Authors: Uehara Koichi , Kurita Siro , Sahashi Norio , Ohmoto Taichi
Published: January 2018

Spore wall morphogenesis of the microspore of Isoetes japonica was studied by transmission electron microscopy. The microspore wall consists of four layers: the perispore, outer exospore, inner exospore, and endospore. The perispore consists of electron‐dense materials. The exospore is divided into outer and inner sections, with a large gap between the two. The outer exospore appears as an undulating plate consisting of tripartite lamellae with homogeneous sporopollenin. The inner exospore consists of an accumulation of tripartite lamellae on the microspore cell membrane. Immediately after meiosis, the tripartite lamellae of the outer exospore forms around the microspore. The lamellated inner exospore forms next, which adheres to the cell membrane of the microspore. The deposition of homogeneous sporopollenin material on the tripartite lamellae causes the plates of the outer exospore to thicken. Some homogeneous material may also be deposited on the inner exospore. Lastly, the electron‐dense perispore is deposited on the outer exospore, and the electron‐lucent endospore forms beneath the inner exospore. We conclude that the lamellae of the outer exospore, inner exospore, and endospore are formed and derived, in that order, from the gametophytic microspore cytoplasm. The homogeneous sporopollenin material of the outer exospore and perispore may be derived from the sporophytic tapetal cytoplasm.
FACTORS AFFECTING RED SPRUCE REGENERATION IN DECLINING AREAS OF CAMELS HUMP MOUNTAIN, VERMONT
Authors: Klein Richard M. , Perkins Timothy D. , Adrian Jeffrey Tricou , Cutler Oates Karen
Published: January 2018

Scarcity of red spruce(Picea rubensSarg.) seedlings in declining spruce‐fir forests of Camels Hump mountain, Vermont, prompted a study on some contributing factors involved in failure of spruce regeneration. Cones were shorter than those from low elevation red spruce trees from unaffected sites. Seed number in cones collected in declining areas of Camels Hump was low as were seed sizes and weights. Seed germination was at control levels only in good seed years. Capacity of seeds to form seedlings was reduced relative to that of controls, although seedling growth was normal. Coniferous litter contains presumed allelopathic substances leachable by contemporary precipitations that affect seed germination and seedling root development in red spruce, but not in balsam fir. Shield fern contains leachable substances that reduce seed germination and seedling root development in red spruce, but not balsam fir. Roots of red spruce germlings have lower capacity to penetrate through the increased forest duff depths of declining forests than do balsam fir roots. It is anticipated that substantial reproduction of red spruce will not occur in declining montane conifer forests under present conditions.
DESICCATION OR FREEZING? MECHANISMS OF WINTER INJURY TO RED SPRUCE FOLIAGE
Authors: Perkins Timothy D. , Adams Gregory T. , Klein Richard M.
Published: January 2018

Selected branches of red spruce{Picea rubensSarg.) saplings growing at 900 m in elevation on Camels Hump Mountain, Vermont, were treated with an acrylic polymer antitranspirant (Adkar Cloud Cover) in October 1989. Winter injury was subsequently apparent on first‐year foliage on 1 February 1990. Addition of antitranspirant significantly increased chloroform extractable wax (plus antitranspirant) weight and cuticle (plus antitranspirant) thickness. The treatment reduced cuticular transpiration under laboratory conditions, but did not lessen the severity of visually apparent winter injury. Xylem water potential of damaged and undamaged branches did not differ. Fresh to dry weight ratios revealed a tendency for damaged needles to desiccate rapidly following winter injury. Foliar pigment concentrations were negatively correlated with severity of winter damage. These results suggest that winter desiccation plays a minor role in inducing winter injury to red spruce foliage.
ECOLOGICAL ASPECTS OF SEX EXPRESSION IN SUBDIOECIOUS SCHIEDEA GLOBOSA (CARYOPHYLLACEAE)
Authors: Sakai Ann K. , Weller Stephen G.
Published: January 2018

The importance of ecological factors such as sex lability, spatial segregation, and resource allocation in the evolution of dioecy were examined in Schiedea globosa. S. globosa is a subdioecious species with equal numbers of plants possessing strictly male or female function and a small proportion of hermaphrodites. The propensity for labile sex expression was under both environmental and genetic control; some plants with male function became hermaphroditic (by producing female flowers) under better growing conditions in the field and in the greenhouse. There was some spatial segregation of the sexes. Because of sex lability, more hermaphrodites than males occurred on moister slopes. Although there were not measurable sex‐related differences in mortality within or between two flowering seasons, more females than males and hermaphrodites occurred at the bottom of slopes. Males and females produced the same number of ramets and inflorescences, but females had a greater number of flowers per inflorescence. Males and females had the same number of ovules (vestigial in males), but females had larger ovules and longer stigmas. Hermaphrodites and males had the same amount of pollen per flower despite the production of fruit by the hermaphrodites. In hermaphrodites, there was no apparent tradeoff within flowers between pollen production and ovule production. These results indicate that spatial segregation, sex lability, and environmental conditions influence allocation patterns of S. globosa, and in combination with high inbreeding depression and selling rates, may promote the further evolution of dioecy in S. globosa.
MATERNAL AND PATERNAL EFFECTS ON FOLLICLE PRODUCTION IN THE MILKWEED ASCLEPIAS SYRIACA (ASCLEPIADACEAE)
Authors: Morse Douglass H. , Schmitt Johanna
Published: January 2018

We measured follicle production from a diallel cross among ten clones of the common milkweed Asclepias syriaca, to assess the relative contributions of maternal and paternal parents. Specific parental combinations differed in the ability to set fruit, indicated by a significant nuclear specific effect accounting for 28% of the observed variance in follicle production. Several mechanisms might contribute to this effect, including shared incompatibility alleles and expression of zygotic genotypes. The nuclear general effect was not significant, however, suggesting a lack of additive genetic variation for offspring control of fruit maturation. Maternal effects also had an important effect on follicle production, as demonstrated by a significant reciprocal general effect (26% of the variance), almost entirely due to a large maternal component. The small reciprocal general variance component attributable to paternal effects, and nonsignificant reciprocal specific effect, indicating little maternal parent‐zygote interaction, suggest that female choice through selective follicle maturation was not important in this experiment. The clones varied in proportion of reproductive output through female function, but a significant tradeoff between male and female success was not detected.
THE ULTRASTRUCTURE OF SAHNIA POLLEN (PENTOXYLALES)
Authors: Osborn Jeffrey M. , Taylor Thomas N. , Crane Peter R.
Published: January 2018

The micromorphology and fine structure of in situ pentoxylalean pollen are described from the holotype of Sahnia laxiphora Drinnan and Chambers 1985 collected from the Lower Cretaceous (Valanginian‐Aptian) of Victoria, southeastern Australia. Pollen grains are ovoid, monosulcate, and relatively small, averaging 26 μm in length. Exine ornamentation is psilate. The sporoderm is two‐parted with the sexine staining lightly throughout and approximately six times the thickness of the more darkly staining nexine. The exine over the sulcus is typically strongly invaginated, and may or may not include an extremely thin sexine layer. The outer part of the sexine is homogeneous, while the inner part is composed of relatively large granules separated by irregular lacunae of various sizes; lacunae are most pronounced at the sexinenexine interface. Faint lamellae characterize the nexine in both apertural and nonapertural regions. Granular orbicules are often associated with the exine surfaces and also occur appressed to pollen sac walls along with lamellated tapetal membranes. Sporoderm ultrastructure is compared to that of nonsaccate pollen of other groups, and particularly to pollen of Bennettitales, Gnetales, angiosperms, and similar plants, to which the Pentoxylales have been thought to be closely related. Although Sahnia laxiphora pollen is not identical to that of any of these taxa, the strongest similarity is with pollen of Bennettitales.
CHLOROPLAST DNA VARIATION IN GLIRICIDIA SEPIUM (LEGUMINOSAE): INTRASPECIFIC PHYLOGENY AND TOKOGENY
Authors: Lavin Matt , Mathews Sarah , Hughes Colin
Published: January 2018

An analysis of chloroplast DNA restriction site variation in Gliricidia sepium reveals two geographically distinct chloroplast lineages, one in the Yucatan Peninsula and the other along the Pacific Coast in Mexico and Central America. Geographical, morphological, biochemical, and habitat distinctions suggest that these two chloroplast lineages reflect organismal lineages. Within the Pacific coastal chloroplast lineage, there exist sublineages that most likely reflect tokogenetic systems of relationship rather than organismal phytogeny, a hypothesis supported by the co‐occurrence of more than one of these chloroplast sublineages in a single population. The genetic distance between any two of these chloroplast lineages ranges from 0.0001 to 0.0024 nucleotide substitutions per site and reveals relatively high levels of intraspecific divergence. We suggest that assessing intraspecific chloroplast DNA variation is important generally in higher level phylogenetic analysis because it enables one to obtain truer estimates of homoplasy, detect potentially cryptic species, and distinguish among molecular markers that reflect phylogenetic vs. tokogenetic relationships. This is in addition to determining the extent of potential complicating factors such as introgression and lineage sorting from polymorphic ancestry.