摘要:

The wind‐dispersed diaspore of the herbaceous perennialCryptantha flava(Boraginaceae) consists of one, or occasionally two, nutlets (seeds) enclosed in a pubescent calyx. Physical characteristics of one‐ and two‐seeded diaspores and their rates of descent in still air were compared. Natural dispersal distances in the field of calyces containing 0, 1, or 2 seeds were also measured. Two‐seeded diaspores are wider at the ovary and have a greater total mass, a greater mass of the ovary, and a higher rate of descent in still air than one‐seeded diaspores. Under field conditions, however, there is no difference in how far calyces containing 0, 1, or 2 seeds disperse. Thus rate of descent is not a good predictor of relative dispersal distances in this species. Much of the dispersal in the field must occur as movement along the surface of the ground, and during such secondary dispersal, the greater width of two‐seeded diaspores may compensate for the potentially opposing effect of their greater mass.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb13509.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

The family Casuarinaceae has been divided recently into four genera on the basis of differences in chromosome numbers, morphological characters including stem morphology, structures of the male and female flowers and fruits, their modern biogeography, and fossil record. All members of the family are characterized by highly reduced leaves, photosynthetic deciduous branchlets, and adaptations to xeric or hot humid environments. The genusGymnostomais characterized by multiple rows of naked stomata along the central vertical faces of the stem internodes.CasuarinaandAllocasuarinadevelop vertically aligned rows of stomata in deep furrows that alternate with stem ridges. Epidermal hairs, formed within the furrows, occur in different species in conformity with other xeric characters. The characters described in this paper conform to the view that the morphological structures represent reduction and specialization rather than primitiveness.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb13510.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

GuraniaandPsiguria, long thought to be dioecious, are actually monoecious; values of Gp, a quantitative measure of an individual's phenotypic gender, are bimodally distributed in natural populations. Individual vines undergo two kinds of sex change: size‐related and intraseasonal. Small (in diameter) plants produce only male flowers; only large plants produce female flowers. In favorable greenhouse situations, plants that reach large sizes switch from all male to female flowering; in poor conditions, the same genotypes remain vegetative or male, or switch back from female condition. Intraseasonal sex change occurs when plants initiate a predominantly female flowering episode with a few functional male inflorescences. Such protandrous vines are usually unisexual any point in time. Since neither type of sex change is obvious without long‐term observations, we suggest that other “dioecious” angiosperms should be more carefully studied.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb13511.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Haplopappus cooperiandChrysothamnus teretifoliusare important elements on alluvial fans in the Owens Valley of California. Selective removal field experiments, followed for 7 months, revealed thatHaplopappuspredawn water potentials were significantly less negative after removal of neighboring plants of either species, whereasChrysothamnuspredawn water potentials were unchanged, compared to controls.Haplopappusalso showed a more dramatic response in water potential following supplemental watering at the end of the dry season. Excavations showed that the root systems of the two species were different: the majority ofHaplopappusroot biomass was within the upper 20 cm of soil, but forChrysothamnusit was below 40 cm depth. Spatial pattern was not always a reliable predictor of biotic interaction in this desert community:Chrysothamnusindividuals were aggregated,Haplopappusindividuals were distributed at random, and plants of the two species were randomly associated.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb13512.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Production of gemmae by gametophytes ofVittariaentails regularity of pattern relevant to systematic comparisons and unusual cellular differentiation relevant to studies of cellular morphogenesis. Cryo SEM allows critical three dimensional analysis of these delicate structures. InVittaria graminifolia, gemmifer cells initiated by the apical meristem typically support two gemma pairs with the terminal gemma of each pair oriented at right angles to the subterminal gemma. Mature gemmae consist of a uniseriate filament of four body cells with rhizoid primordial cells at each end. Cellular differentiation during gemma production includes growth from specific, localized areas, constricted connections between cells, reorientation of the polarity of cell growth, temporary suppression of cell growth and division, abscission between cells, and deposition of surface material on mature gemmae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb13513.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Seed set in naturally pollinated flowers of the alpine skypilot,Polemonium viscosum, is influenced by two components of pollination quality: the number of outcross pollen grains received by a flower over its lifetime and the purity, or percentage of conspecific grains in the pollen mixture. Plants of this species have flowers that are either sweet or skunky in scent. Sweet flowers are larger on average than skunky ones. In populations frequented by a fly‐dominated assemblage of pollinators, skunky‐scented flowers tended to receive more outcross pollen than sweet‐scented flowers, regardless of their size. In contrast, in predominantly bumble bee‐pollinated populations, floral scent and size were both correlated with pollination quality. These results illustrate that advantages associated with flower phenotypes are habitat dependent. With bumble bee pollination, plants having large sweet‐scented flowers received purer pollen mixtures and more outcross grains than neighboring plants with smaller skunky‐scented flowers. When variation in pollination quality with flower size was accounted for statistically, floral scent differences remained correlated with differential outcross pollination. While both flower scent and size are secondary attractants, they affect independent components of pollination quality and have complementary effects on seed set.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb13514.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Instead of alternating as is typical for the majority of flowering plants, the five stamens ofBasella rubraare superposed to the five tepals. The first two tepals toward the abaxial side are initiated first, followed by the two tepals toward the adaxial side and the abaxial tepal that may be lagging behind. Stamen inception mirrors that of the petals, i.e., the two stamens toward the abaxial side are initiated first, followed by those toward the adaxial side and the abaxial one that may be lagging behind. Existing phyllotaxis theories do not seem to fully explain this pattern of petal‐stamen superposition. Apart from the Basellaceae, superposition between perianth members and stamens or stamen fascicles occurs in about 13% of all families of flowering plants, although in some of them it is restricted to only a few members. Other floral patterns that also resist explanation in terms of existing phyllotaxis theories are briefly discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb13515.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

In Angiosperms placentae or ovules are formed on carpels or the floral apex. Hence, in a developmental sense, there are carpellate and acarpellate gynoecia. The latter occur in about 11% of all Angiosperm families.Basella rubrais an example of the noncarpellate condition. Its single basal ovule is formed directly from the floral apex. In young developmental stages it even retains the tunica‐corpus organization of the floral apex. In later developmental stages, three septa arise only at the base of the ovule. The single vascular strand of the ovule is symmetrically derived from the bases of all six strands that supply the ovary wall, i.e., it is not associated with the vascular strand of only one of the three gynoecial appendages. Hence, neither development nor vascularization support a carpellate interpretation of theBasellagynoecium. With regard to the evolution of basal placentation inBasellaand other taxa of Angiosperms three possibilities exist: 1) It is derived from the carpellate condition, 2) It is primitive and the carpellate condition is derived, 3) Both carpellate and noncarpellate organizations have coexisted during the evolution of Angiosperms which may have been monophyletic or polyphyletic.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb13516.x

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

The sources, uptake, and assimilation of nitrogen by plants has a history that dates from the time of the ancient Greeks, and the elucidation of the interlocking questions occupied some of the finest philosophical and scientific minds of Europe for considerably longer than two millenia. Current acidic precipitation, containing a significant amount of nitrogen, has again focused attention on the role of precipitation nitrogen in plant nutrition.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb13517.x

出版商:Wiley    

年代:1988

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1988.tb13518.x

出版商:Wiley    

年代:1988

数据来源: WILEY