摘要:

Reproductive mode and chromosome numbers were determined for populations of several species ofCalamagrostisfrom eastern North America.Calamagrostis pickeringii(2n= 28),C. perplexa(2n= 70),C. porterisubsp.porteri(2n= ca. 88–100) andC. porterisubsp.insperata(2n= 56) all have a sexual pattern of megagametophyte formation; the basal megaspore of a tetrad develops into aPolygonum‐typeembryo sac with proliferating antipodal cells characteristic of the Gramineae. In these four taxa self‐incompatability, population structure and infrequent flowering limit seed production; they persist primarily by rhizomes and occupy relatively stable, late‐successional habitats.Calamagrostis strictasubsp.inexpansaincludes apomictic variants (2n= ca. 104–123)that produce megagametophytes by diplospory; the single archesporial cell divides mitotically to produce an embryo sac appearing identical to those formed by sexual species. The embryo and endosperm develop autonomously from egg cell and polar nuclei, respectively. Some apomictic individuals occasionally produce some pollen and may have the potential for reproducing sexually. Their seed set insured by apomixis, variants of subsp.inexpansacolonize disturbed, open habitats and have achieved wide distributions in glaciated regions of North America. Reinterpretation of relationships among taxa I examined necessitates the following new nomenclatural combinations;C. porterisubsp.insperata(Swallen) comb. nov. is based onC. insperataSwallen;C. strictasubsp.inexpansa(A. Gray) comb. nov. is based onC. inexpansaA. Gray and includesC. lacustris(Kearney) Nash andC. fernaldiiLouis‐Marie.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12516.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

The plastochron index (PI) was developed forVitisand related to lamina K+concentration. The concentration of lamina K+declined with increase in leaf age and PI, whereas total lamina K+content increased. Part of the decline in lamina K+concentration was attributed to an initial decrease in lamina density. Therefore, expression of K+concentration on a leaf area basis is recommended rather than on a dry weight basis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12517.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Foliar extracts of high elevationQuercus rubracontain 20 major flavonol‐3‐0‐glycosides based primarily on the aglycones myricetin, quercetin, and kaempferol. These compounds display an altitudinal cline in the Appalachian mountains, with quercetin‐rich low elevation chemotypes intergrading into myricetin‐rich high elevation forms. These chemotypes appear to be correlated with previously documented variation in foliar morphology. The degree of interpopulation variation also differs with elevation. At higher elevations flavonoids differ only quantitatively between sites, while below 3,000 ft there is site‐to‐site variability in the hydroxylation level of the aglycones.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12518.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Microsporogenesis, pollen germination and fertility of males gametes were studied in 24 artificial intergeneric and interspecific F1hybrids of orchids. Although parental species had the same chromosome number (2n= 40), microsporogenesis of the hybrids was irregular due to the lack of homology of the chromosomes of the parental species. This led to formation of tetrads of microspores without micronuclei, tetrads with 1–8 micronuclei, triads, dyads with and without micronuclei, and monads. Chromosomes numbers found in haploid microsporocytes ranged from 7 to 40; in micronuclei the chromosome number varied between 1 and 5.In terms of pollen germination, three situations were observed: 1) hybrids whose pollen grains did not germinate in the stigma; 2) hybrids in which the pollen tubes grew down in the style, but did not penetrate into the ovary; 3) hybrids in which the pollen tubes grew down normally through the ovary, reaching the ovules. When the pollen tubes did not penetrate the ovary no fruit was formed. Therefore germination tests carried out in vitro may not indicate pollen fertility, because pollen tube growth in the style of the flower may be insufficient to induce fruit formation or to accomplish fertilization.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12519.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

This report investigates the physiological basis for the production of dimorphic leaves on the aquatic angiospermCallitriche heterophylla.In nature, the leaf morphology of this plant depends on whether the shoot apex is submerged in or emergent from water. The water‐form leaves that develop on submerged apices assume a long, linear shape in contrast to the short, obovate appearance of land forms on emergent apices. The parameters of length/width ratio and stomatal density were used as developmental indices to characterize how natural conditions, fluctuating water levels and other experimental treatments affect leaf shape. Transferring submerged and emergent shoots to the alternative culture conditions caused immature leaves to assume the characteristics appropriate to their new environment. Moreover, the treatments of 0.24 mol mannitol, high temperature (30 C) and 10−‐5m abscisic acid induced submerged shoots to produce land‐form leaves whereas 10−‐5m gibberellic acid mediated the development of water‐form leaves on emergent shoots. Water, osmotic and pressure potentials of immature leaves in the control and experimental treatments were determined by thermocouple psychrometry. Under natural conditions, growing water forms exhibited high turgors (3–5 bars) while developing land forms showed much lower turgors (0–1 bar). Similar correlations between turgor pressure and leaf morphology were observed in the case of the gibberellic acid and mannitol treatments. However, abscisic acid and high temperature caused the developing land‐form leaves to exhibit high turgors without a concomitant change to the water‐form morphology. Microscopic measurements of epidermal cells established that irrespective of the experimental conditions, water‐form leaves had longer and narrower epidermal cells with less convoluted anticlinal walls than land forms. Cell counts indicated that the numbers of epidermal cells did not account for the observed differences in leaf morphology. The results are interpreted in terms of how cell expansion might regulate leaf morphology in aquatic angiosperms.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12520.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

The leaf ofPyrossia longifolia(Burm.) Morton, an epiphytic fern known to exhibit CAM, was examined by light and electron microscopy. The relatively thick leaf contains a single‐layered epidermis, “water‐storage” tissue, and a reticulate vascular system embedded in mesophyll tissue not differentiated into palisade and spongy layers. Mesophyll is composed of large, slightly elongate cells each with a thin, parietal layer of cytoplasm and a large central vacuole. The chloroplast‐microbody ratio in mesophyll cells indicates thatPyrossiamay be a high photorespirer and thus similar in that sense to C3plants. Mesophyll is separated from the vascular tissue by a tightly‐arranged layer of endodermal cells with Casparian strips. The inner layer of mesophyll cells and the endodermal cells lack suberin lamellae. The collateral veins contain sieve elements, tracheary elements, pericycle and vascular parenchyma cells, the latter conspicuously larger than the sieve elements. The vascular parenchyma is the only cell type in the leaf which contains plastids with a peripheral reticulum. The parenchymatic elements of the leaf are connected by plasmodesmata, all of which lack neck constrictions and sphincters, or sphincter‐like structures. The connections between sieve elements and adjacent parenchymatic elements are pore‐plasmodesmata characterized by prominent wall thickenings on the parenchymatic‐element side of the wall. The distribution and relative frequencies of plasmodesmata between the various cell types of the leaf indicate photoassimilates may move either symplastically or by a combination of symplast and apoplast from the mesophyll to the site of phloem loading in the veins.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12521.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Abundance, species composition, and distribution of buried seeds in a San Francisco Bay salt marsh were studied by collecting soil samples in October and February and observing seedling emergence in the greenhouse. Results were compared with existing vegetation patterns and field germination. Average numbers of buried viable seed down to a 5‐cm depth were 380/ m2in October and 700/m2in February, with field germination averaging 118/m2.Salicornia virginicadominated the seed bank in the greenhouse and in field germination. Most other marsh species were present in the seed bank but numbers of seeds were low. A significant correlation was found between highest species diversity and proximity to channels. The nature of this low‐diversity, low‐density seed bank reflects dominance of long‐lived perennial species, seed dispersal patterns and selective environmental pressures.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12522.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Comparisons are presented between the three‐dimensional airflow patterns created around and by a scale model of a conifer ovulate cone and the trajectories of windborne pollen grains aroundPicea, Larix,andPinusovulate cones. Three general components of the airflow pattern around an ovulate cone model are 1) doldrum‐like eddies, rotating over the adaxial surfaces of cone scales and directed toward attached ovules, 2) airflow spiralling around the cone axis along cone scale orthostichies and parastichies, and 3) a complex pattern of vortices (“umbilicus”) directed toward the leeward surface of the ovulate cone. The observed trajectories of pollen grains around cones ofPicea, Larix,andPinusconform to two of these three airflow components: 1) pollen grains are seen to roll along cone scales toward the distal scale margin and to become reentrained in airflow directed backward toward attached ovules, and 2) pollen grains passing around the cone are deflected into the “umbilicus” airflow pattern, where they either settle on or impact with cone scales (approach trajectories), or where they approach the leeward cone surface but are deflected away by airflow passing under the cone (Z‐shaped trajectories). Vectoral analyses of pollen grain motion reveal a complex pattern of trajectories influenced by boundary layer conditions defined by ovulate cone geometry and ambient airflow speed. Wind tunnel studies of ovulate cones subtended by leaves and stem indicate that leaves circumscribing the cone act as a snowfence, deflecting windborne pollen toward the cone.Vectoral analyses of airflow patterns and pollen grain trajectories close to ovulate cones indicate that wind pollination in conifers is a non‐stochastic aerodynamic process influenced by cone‐leaf morphology and the behavior of pollen grains as windborne particles.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12523.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Based on the ready availability of nectar and pollen, and on the large numbers and great diversity of insect visitors, species in the Apiaceae have been labeled promiscuous. The distinction between floral visitors and effective pollinators, however, is extremely important and is rarely discerned. Floral visitation was documented for plants of nine populations in a comparative study of three species of the closely related apioid genera,ThaspiumNutt. andZiziaKoch. A pollinator importance index was calculated for each floral visitor using visitor abundance, pollen load composition and foraging behavior as its basic components. Results showed that, despite a high diversity of insect visitors, generally 1–4 species accounted for a minimum of about 74% of the pollinations in all populations. This specialization in pollination appears in part to be the result of an oligolectic relationship betweenAndrena ziziae(Hymenoptera; Andrenidae) and plants of the taxa studied, but solitary bees of Andrenidae, Colletidae and Halictidae in general were efficient and important pollinators. This study emphasizes that visitation records, when considered alone, effectively disguise specialization in the pollination system.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12524.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

We report on the leaves, fruits, inflorescences, and pollen of two fossil species in the genusPlatycarya.The association of these dispersed organs has been established by their repeated co‐occurrence at a large number of localities, and for two of the organs (fruit and pistillate inflorescence, and pollen and staminate inflorescence) by apparent organic attachment of compression fossils. Each of the two species can be distinguished by characteristics of all the known megafossil organs. We also review the fossil record of dispersed platycaryoid fruits and inflorescences, recognizing three additional species ofPlatycaryaand two ofHooleya.Two of the fossilPlatycaryaspecies are morphologically very different from the livingPlatycarya strobilaceaSieb. et Zucc., but they show the diagnostic features of the genus.Hooleyais a generalized member of the Platycaryeae that is probably close to the ancestry ofPlatycarya.The twoPlatycaryaspecies known from multiple organs provide a remarkable example of mosaic evolution in which fertile and foliar structures have attained different levels of morphological specialization. The leaves, often considered the most plastic of plant organs, retain several features that are otherwise seen only in the Engelhardieae. These similarities in leaf architecture between the fossilPlatycaryaspecies and Engelhardieae are advanced features for the Juglandaceae, and thus indicate a sister‐group relationship between the two lines. In contrast to the leaves, the fruits, inflorescences, and pollen of the fossilPlatycaryaspecies are almost as specialized as those of the extantP. strobilaceaand bear little resemblance to the same structures in other genera of the family.The morphology, taphonomy, sedimentary setting, and geographic and stratigraphic distribution of three of the fossil platycaryoid species suggest that they were wind‐dispersed, early successional plants that grew in thickets. This habit is retained byPlatycarya strobilaceaand is typical of many of the amentiferae (e.g. Myricaceae, Betulaceae). Ther‐selected life‐history pattern of thePlatycaryaline may well have contributed to its low diversity through geologic time.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12525.x

出版商:Wiley    

年代:1984

数据来源: WILEY