摘要:

Scanning electron microscope (SEM) studies of paraffin‐sectioned material of stems and roots ofBarclaya rotundifoliaHotta revealed perforations on tracheary elements of roots, but not on those of stems. End walls of vessels are identical with lateral walls except for the presence of perforations. Perforations can only be clearly revealed with SEM, and this method is advocated for further study of tracheary elements of Nymphaeaceae in particular, and primary xylem of ∗∗∗angiosperms in general. Vessel presence may be related to the habitat of this species, which unlike other members of the Nymphaeaceae (sensu stricto) has only aerial leaves and a rhizomatous system that is not inundated for prolonged periods.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12670.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Maximum vessel diameters were examined in the secondary xylem of stems ofGnetumof various sizes. One tree (G. gnemon) and 13 liana species were compared. In three species, vessel length distributions were determined by the latex paint method, and showed many short and fewer long vessels. Latex and compressed air methods, used to find the maximum vessel lengths, showed that maximum vessel lengths were similar for three species ofGnetum.In old stems, mean and maximum vessel diameters tended to be greater in lianas than in the tree species. The skewed distribution of vessel lengths and the trend of wider vessels in lianas as compared to trees were similar to those distributions and trends described previously for angiosperms. In random samples of macerated wood of three species, simple perforation plates were most common in vessel members of all species. Foraminate and modified foraminate perforations were less frequent. Average diameter of vessel members with either foraminate or modified foraminate perforations was less than for those with simple perforations. The resemblance ofGnetumvessels to those of angiosperm trees and vines is most likely a case of convergent evolution (homoplasy) in xylem characteristics.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12671.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

The thallus of the lichenRamalina menziesiiTayl. is composed of net‐like units that develop by diffuse expansion of perforated tissue produced at the net apex. Study of net tissue with transmission electron microscopy reveals that the cortical cells are surrounded by a succession of cell walls alternating with layers of an electron‐transparent matrix substance. In the course of thallus growth the cortical cell walls are continually deformed and new ones constructed. The deposition of new walls and matrix layers displaces the older walls centrifugally from the cell. Electron‐dense boundaries develop at the interfaces among cells where the remains of the oldest walls are compressed against those of neighboring cells. As new branch cells are inserted through the concentric accumulations, the dense boundaries appear to enclose fascicles of cells, visible in cross section with light microscopy. Cortical organization inRamalina menziesiiis contrasted with that reported in other lichens, and a functional relationship to diffuse growth of the thallus is suggested.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12672.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

A 1,288 ± 271‐yr‐old (1,350 ± 220 yr BP, radiocarbon age) seed of Sacred Lotus (Nelumbo nuciferaGaertn.) from an ancient lake bed at Pulantien, Liaoning Province, China, has been germinated and subsequently radiocarbon dated. This is the oldest demonstrably viable and directly dated seed ever reported, the preserved relict of one of the early crops of lotus cultivated by Buddhists at Pulantien after introduction of the religion into the region prior to 372 A.D. A small portion of the dry pericarp of a second lotus fruit from the same locale has been dated as being 332 ± 135‐yr‐old (270 ± 60 yr BP, radiocarbon age) by accelerator mass spectroscopy at the Lawrence Livermore National Laboratory. This polycentenarian seed not only germinated but is still growing (since March, 1994). Of six old lotus fruits tested, two‐thirds germinated, almost all in fewer than 4 d, as rapidly as fruits harvested from the progeny of Pulantien Sacred Lotus plants (under cultivation by the National Park Service in Washington, DC), and more rapidly than fresh fruits of Yellow Lotus [N. lutea(Willd.) Pers.]. Growth of the old lotus is robust: rhizome formation and leaf emergence at rhizome nodes are more rapid than those of the Pulantien progeny, although the leaf width is smaller. Activity of the protein‐repair enzyme L‐isoaspartyl methyltransferase in the old lotus seed is persistent during germination and is as robust as that in the progeny, and the degree of aspartyl racemization in proteins of the two groups of plants is minimal and essentially identical. The six dated ancient Sacred Lotus fruits range in age from 95 to 1,288 yr (with a mean age of 595 ± 380 yr), evidently reflecting their production, deposition, and preservation at varying times during the intervening millennium.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12673.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Selfing variants in tristylousEichhornia paniculata(Pontederiaceae) possess an elongated, short‐level stamen adjacent to mid‐level stigmas, which causes autonomous selfing. The variants commonly spread in dimorphic, but not trimorphic populations in northeast Brazil. We investigated the effect of stamen elongation on pollen size and siring ability. Competition experiments using controlled hand‐pollination and allozyme markers were used to compare different pollen types. Pollen from the elongated stamen was significantly larger in size than pollen from unmodified short‐level stamens. In mixed pollinations of mid‐level stigmas, pollen from the elongated stamen sired significantly more seed than pollen from unmodified short‐level stamens. Despite these differences, the size and compatibility of pollen from the elongated stamen were more similar to short‐ than mid‐level pollen, indicating that alterations to stamen level were not associated with major changes in pollen characteristics. The results suggest that the advantage of selfing variants in dimorphic populations is mainly due to efficient pollen transfer to mid‐level stigmas rather than increased postpollination siring success of pollen from modified stamens. In addition, the absence of major changes in pollen size and compatibility associated with stamen elongation support other lines of evidence indicating that selfing variants are not the result of recombination in the putative heterostyly supergene.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12674.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Selection on male function has been invoked to explain various floral features, including number of flowers, flower size, and flower color. Here I describe two experiments designed to examine the efficiency of distyly in promoting male floral function, as measured by successful pollen dispersal to stigmas. In both experiments, I performed emasculations to control the type of pollen locally available in a natural population ofPsychotria suerrensis, a tropical shrub. In the “natural‐recipients” experiment, I allowed each floral morph to donate pollen on alternate days to emasculated flowers of each morph. In the “paired‐recipients” experiment, I attached paired cuttings of each morph to individual donor plants. The results of both methods were consistent. Pollen borne on low anthers (from pin plants) was transferred most efficiently to low stigmas (on thrum plants). Pollen borne on high anthers (from thrum plants) was dispersed in equal amounts to flowers of both morphs. The results suggest that distyly is only partially effective in achieving efficient pollen donation. Male function of pins is enhanced by the polymorphism, but male function of thrums is not. A supplemental pollination experiment illustrates that seed set in this species is predominantly pollen limited, reducing the importance of male function, in comparison with species where seed set is primarily resource limited.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12675.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

To test hypotheses on the evolution of functional relationships, phenotypic correlations among floral traits were estimated in five species of insect‐pollinated plants. The species studied were wild radish (Raphanus raphanistrum), canola (Brassica napus), phlox (Phlox divaricata), dame's rocket (Hesperis matronalis), and black mustard (Brassica nigra). Six floral traits were measured on each species. In three of the five species the correlations between the filaments and corolla tube were significantly greater than the other floral correlations. This result is consistent with the hypothesis that selection for proper anther placement to enhance pollination has increased the filament‐corolla tube correlations in these three species. In contrast, none of the species showed evidence of selection for an optimal stigma placement; the correlations between the pistil and corolla tube lengths were not greater than the other floral correlations in any of the five species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12676.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

AlthoughRhododendronspp. anthers have apical pores and should be expected to be buzz pollinated, bees do not normally sonicate them to release pollen. Stamens were examined to determine their pollen release mechanism; the filaments were shown to have natural vibration modes that cause pollen to be forcibly ejected by vibration, providing the pollen is mature. The first natural vibration mode of the stamens was found to generate centrifugal force sufficient to throw the pollen toward the apical pore and out of the anther, so that it adheres to the anther tip and hangs in the bee's path to the nectaries. These vibrations may be triggered by bees brushing past the long stamens when foraging for nectar, so that the flowers retain their pollen until insect vectors begin foraging on them. The low frequency vibration modes of the viscin threads, which hold the pollen together, may contribute towards the pollen ejection by low frequency stamen vibration. Vibration transmission of dehiscent anthers containing pollen was good from 50 Hz to 850 Hz, suggesting that sonication should be an efficient method of pollen collection, although this rarely occurs. Vibratory ejection occurs at a constant energy level, rather than the constant force levels found in previous research onActinidia.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12677.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

We studied intraspecific variation in samara morphology and flight behavior within and among parent trees ofAcer saccharinum(silver maple), with a particular focus on the effect of samara shape. Samara mass, area, wing loading, and descent rate from a 4.5‐m indoor balcony were measured for 50 undamaged mature samaras from each of six parents. We found significant differences among parental types for all morphological variables and descent rate. These differences yielded a 50% range in mean dispersal potential among the six parents. There was a strong linear correlation between descent rate and square root of wing loading when mean values were plotted for each of the six parental types. But there was considerable within‐parent variation for all measured variables, including substantial nonallometric variation in wing loading caused in part by poor correlations between wing area and fruit weight. Parents also differed widely in the relationship between square root of wing loading and descent rate (linearr2= 0.150‐0.788), with one parental type showing no significant relationship. Fruits from the same parent with similar values of the square root of wing loading showed as much as a 75‐100% difference in descent rate. The usefulness of mass : area indices such as wing loading is limited by its exclusion of aerodynamically important factors such as mass distribution and wing shape, which in our case caused the six parents to behave aerodynamically almost as if they were six separate species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12678.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Analyses of fine‐scale and macrogeographic genetic structure in plant populations provide an initial indication of how gene flow, natural selection, and genetic drift may collectively influence the distribution of genetic variation. The objective of our study is to evaluate the spatial dispersion of alleles within and among subpopulations of a tropical shrub,Psychotria officinalis(Rubiaceae), in a lowland wet forest in Costa Rica. This insect‐pollinated, self‐incompatible understory plant is dispersed primarily by birds, some species of which drop the seeds immediately while others transport seeds away from the parent plant. Thus, pollination should promote gene flow while at least one type of seed dispersal agent might restrict gene flow. Sampling from five subpopulations in undisturbed wet forest at Estación Biologíca La Selva, Costa Rica, we used electrophoretically detected isozyme markers to examine the spatial scale of genetic structure. Our goals are: 1) describe genetic diversity of each of the five subpopulations ofPsychotria officinalissampled within a contiguous wet tropical forest; 2) evaluate fine‐scale genetic structure of adults ofP. officinaliswithin a single 2.25‐ha mapped plot; and 3) estimate genetic structure ofP. officinalisusing data from five subpopulations located up to 2 km apart. Using estimates of coancestry, statistical analyses reveal significant positive genetic correlations between individuals on a scale of 5 m but no significant genetic relatedness beyond that interplant distance within the studied subpopulation. Multilocus estimates of genetic differentiation among subpopulations were low, but significant (Fst= 0.095). SignificantFstestimates were largely attributable to a single locus (Lap‐2). Thus, multilocus estimates ofFstmay be influenced by microgeographic selection. If true, then the observed levels of IBD may be overestimates.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12679.x

出版商:Wiley    

年代:1995

数据来源: WILEY