摘要:

The air disturbance patterns created by and around the ovules ofTaxus cuspidataare quantified for various orientations to the direction of ambient airflow, and are shown to largely dictate the motion (vectoral trajectories) and mode of deposition of windborne pollen on ovule surfaces. Perpendicular orientation to the direction of airflow results in two regions characterized by high densities of adhering pollen — one on the windward surface of the ovule, resulting from direct inertial collision, and another on the leeward surface resulting from non‐inertial sedimentation. Parallel and inclined orientations of the ovule to the direction of airflow produce quantitative and qualitative variations in the pattern of adhering pollen resulting from inertial and non‐inertial deposition. Direct collision of windborne pollen grains with the micropylar ends of ovules occurs for all orientations to wind direction. The aerodynamics of the ovulate shoot complex ofTaxus cuspidatais related to that previously described for conifer ovulate cones, cycad megastrobili, and simulated wind tunnel analyses of archaic Paleozoic ovules based on scale models. Water transport of pollen (adhering to integument and bract surfaces) to micropyles quantitatively alters the distribution of adhering pollen grains on ovule surfaces. Although there is no evidence that pollen grains of this species are osmotically ruptured, observations do not preclude the possibility that water transport of pollen may reduce the number of viable pollen grains reaching the micropyle.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05339.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Leaves ofAlternanthera philoxeroides, alligator weed, developed at a photosynthetic photon flux density (PPFD, light energy at wavelengths of 400 to 700 nm) of 790 μmol sec−1m−2(High Light) had less surface area, were thicker, had a higher maximum Pn(net rate of CO2uptake), and required a higher PPFD for saturation of Pn, than leaves developed at 160 μmol sec−1m−2(Low Light). Mesophyll thickness at Low Light was within 19% of maximum 2 days after emergence but at High Light, thickness increased 79% between 2 and 16 days after leaf emergence. The ratio of mesophyll surface area to leaf surface area decreased during development in both light treatments; the ratio, however, was over 70% greater in fully expanded High Light leaves than in Low Light leaves. Maximum Pnexpressed on a leaf surface area basis was 158% greater in High Light leaves than in Low Light leaves, but Pnwas only 58% greater when expressed on a mesophyll surface area basis. It was estimated that fully expanded High Light leaves fixed 72% more CO2per leaf (Pnexpressed per unit surface area times the total surface area per leaf) than fully expanded Low Light leaves when Pnwas measured at the PPFD leaves expanded under. Both High and Low Light leaves would fix about the same amount of CO2per leaf when Pnwas measured at 160 μmol sec−1m−2because the larger surface area of the Low Light leaves offset small differences in Pn.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05340.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

All flowers ofAnemopsis californica, the most specialized taxon of the family Saururaceae, are initiated as individual primordia subtended by previously initiated bracts, in contrast to the common‐primordium initiation of all flowers ofSaururus cernuusand of most flowers ofHouttuynia cordata.Floral symmetry is bilateral and zygomorphic, and the sequence of initiation among floral parts is paired or whorled. InA. californica, the six stamens arise as three common primordia, each of which later bifurcates to form a pair. The three common primordia occupy sites corresponding to the positions of the three stamens inH. cordataflowers. InAnemopsis, the filaments of each pair are connate. Each stamen pair is vascularized by a single bifurcating vascular bundle. The three carpels per flower are usually initiated simultaneously although there may be some variation. Adnation between stamens and carpels results from zonal growth. Downward extension of the locule, and proliferation and expansion of receptacular tissue and inflorescence cortical tissue around the locule below the bases of the carpels produce the inferior ovary. The inflorescence terminates its activity as a flattened apical residuum, surrounded by bracts subtending reduced flowers most of which have stamens only.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05341.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Mathematical models estimated that xenogamy accounted for 7% and 35% of the stigmatic pollen loads ofIpomoea hederaceaandI. purpurea, respectively, in experimental populations. The xenogamy estimate forI. hederaceaagreed closely with outcrossing estimates previously reported for this species. The discrepancy between the xenogamy estimate and the previously reported outcrossing estimate forI. purpureacould be explained by differing pollinator flight patterns between experimental and natural populations and/or by selection for cross pollen in the pistil ofI. purpurea.Interspecific pollen flow fromI. purpureato emasculated flowers ofI. hederaceareduced seed production in the latter. The possible significance of interspecific pollen flow fromI. purpureafor the evolution of autogamy inI. hederaceawas discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05342.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

The formation of anomalous, binucleate pollen grains and their subsequent embryogenic development, induced by anther culture inHyoscyamus niger, were analyzed by transmission electron microscopy (TEM). In culture, uninucleate pollen grains occasionally divided symmetrically giving rise to two apparently identical nuclei sharing a common cytoplasm. These nuclei divided once or twice unaccompanied by cell wall formation. After the daughter nuclei organized into cells, their subsequent division products contributed to embryoid formation. In conjunction with previous studies of pollen embryogenesis inH. niger, it appears that in contrast to the principle mode of embryogenesis (i.e., first asymmetric division forms typical two‐celled pollen grain and the generative cell acts as the embryogenic precursor), anomalous pollen show no carry‐over of gametophytic influences following embryogenic induction. This suggests that specific pathways of embryogenesis are correlated with the rate at which gametophytic gene activity is repressed following induction.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05343.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Camellia japonicais a widespread and morphologically diverse tree native to parts of Japan and adjacent islands. Starch gel electrophoresis was used to score allelic variation at 20 loci in seeds collected from 60 populations distributed throughout the species range. In comparison with other plant species, the level of genetic diversity withinC. japonicapopulations is very high: 66.2% of loci were polymorphic on average per population, with a mean number of 2.16 alleles per locus; the mean observed and panmictic heterozygosities were 0.230 and 0.265, respectively. Genotypic proportions at most loci in most populations fit Hardy‐Weinberg expectations. However, small heterozygote deficiencies were commonly observed (mean population fixation index = 0.129). It is suggested that the most likely cause of the observed deficiencies is population subdivision into genetically divergent subpopulations.The overall level of population differentiation is greater than is typically observed in out‐breeders: The mean genetic distance and identity (Nei's D and I) between pairs of populations were 0.073 and 0.930, respectively, and Wright's Fst was 0.144. Differences among populations appeared to be manifested as variation in gene frequencies at many loci rather than variation in allelic composition per se. However, the patterns of variation were not random. Reciprocal clinal variation of gene frequencies was observed for allele pairs at six loci. In addition, principal components analysis revealed that populations tended to genetically cluster into four regions representing the geographic areas Kyushu, Shikoku, western Honshu, and eastern Honshu. There was a significant relationship between genetic and geographic distance (r = 0.61; P<0.01). Analysis of variance on allozyme frequencies showed that there was approximately four times as much differentiation among populations within regions, as among regions. It is likely that the observed patterns of population relationships result from the balance between genetic drift in small subpopulations and gene flow between them.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05344.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

The ontogeny of the shoot and the tendril‐bearing leaf was studied in four species ofSmilaxwhich differ considerably in growth habit. Growth is indeterminate inS. bona‐nox, S. rotundifolia, S. laurifoliaand determinate inS. pumila.Shoot apical organization in all four species is consistent with the tunica‐corpus concept. The number of tunica layers varies from 2 inS. bona‐nox, S. pumila, andS. rotundifoliato 3 (2–4) inS. laurifolia.A primary thickening meristem was observed in 5.laurifolia.Shoot tip abortion involving a cessation of vegetative growth resembling that found in many woody plants occurs inS. pumila.Even though there are distinct differences in growth habit, vigor, and anatomy, the four species share many developmental similarities. Hence, subtle changes in apical ontogeny may be associated with marked differences in habit.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05345.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Scanning electron microscopy observations of the spores ofBruchiahave resulted in the recognition of four spore types based on the ornamentation of the distal spore surface: warty or verrucate, pitted, reticulate, and spinose. The proximal surface of the spores of all species, exceptB. brevipes, is characterized by a central aperture region surrounded by a triangular murus or rows of spinae forming a triangle and 1 or 2 smooth or verrucate collars. The ornamentation patterns observed are considered to be characteristic for the genus. Spore morphology alone can rarely be used to distinguish species but in conjunction with certain other characteristics, it is an important taxonomic feature. Spore morphology is a major characteristic used to define the limits of the highly variable speciesB. flexuosa(spinose spores) and to distinguish it from the closely related speciesB. texana(reticulate spores). Variations in ornamentation patterns within the genus support the recognition of two subgenera (subgenusBruchiaand subgenusSporledera). Spore morphology also supports the close relationship betweenBruchiaandTrematodonand is sufficient to eliminate several questionable taxa from the genus.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05346.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

A rhizomorph ofPaurodendronwith an intact apex recently has been discovered in Upper Pennsylvanian sediments of Ohio, and this provides the anatomical evidence necessary to interpret structure, ontogeny and homologies among lycophyte rooting organs. The basal meristem ofPaurodendronis radial and lenticular, and produces an apical plug of parenchymatous tissue similar to a root cap. The plug is surrounded by a furrow associated with radially aligned cells that demonstrate a developmental correspondence to the furrow(s) ofIsoetes.Based on external structural similarities at the rhizomorph apices ofPaurodendron, Stigmaria, and youngNathorstiana, and on the anatomical similarities ofPaurodendrontoIsoetes, Stigmaria, Chaloneria, andLepidocarponembryos, all are interpreted as having a rooting organ that represents a modified shoot system that is fundamentally unlike the primary root system of seed plants. Likewise, the rootlets of rhizomorphic lycophytes are interpreted as leaves modified for rooting, and that have the equivalent of exogenous origin. As such, they are fundamentally unlike the adventitious roots of rhizomatous lycophytes likeLycopodiumandSelaginella.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05347.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Field‐collected nodules ofComptonia peregrina(L.) Coult. andMyrica galeL. (Myricaceae), infected by the nitrogen‐fixing actinomyceteFrankiasp., were of two types: those that lacked sporangia entirely, designated spore(‐), and those that showed extensive sporangial development, designated spore(+). In spore(+) nodules ofC. peregrina, sporangia began to develop after the differentiation of endophytic vesicles and the concomitant onset of nitrogenase activity. At the onset of sporangial differentiation, infected host cells appeared healthy. However, endophytic vesicles and host cell cytoplasm and nuclei began to senesce rapidly as sporangia developed. Staining of sectioned material with the fluorescent stain Calcofluor White suggested that vesicles, hyphae and young sporangia were enclosed within a host‐derived encapsulation layer, but mature sporangia were no longer encapsulated. In bothC. peregrinaandM. gale, vesicles were more short‐lived in spore(+) than in spore(‐) nodules. Field‐collected spore(+)M. galenodules exhibited a pronounced seasonality of sporangial formation. Sporangia began to differentiate in June, after the formation of vesicles and became more prominent in late summer. Inter‐ and intraspecific cross‐inoculations suggest that the ability to form sporangia in the symbiotic state is controlled by endophytic strain type rather than host genotype or host/endophyte combination. The host may, however, influence the number and seasonal appearance of sporangia formed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb05348.x

出版商:Wiley    

年代:1985

数据来源: WILEY