THE POSSIBLE ROLE OF A FIBROUS BODY IN THE GENERATIVE CELL OF THE POLLEN GRAIN OF TILLANDSIA CAPUT-MEDUSAE MORR. (BROMELIACEAE)

The occurrence of a fibrous body in the generative cell of the pollen grain of Tillandsia caputmedusae Morr. (Bromeliaceae) is pointed out and its possible role is indicated.     

OBSERVATIONS ON THE MICROBODIES IN THE GENUS TILLANDSIA (BROMELIACEAE)

Organelles morphologically similar to microbodies have been found in several tissues of atmospheric species of Tillandsia from different habitats. The presence of catalase was demonstrated by the DAB reaction thus confirming the microbody nature of these organelles. They are a feature of the Tillandsia species with normal photosynthetic carbon fixation and with CAM. Their size is consistently small. The nucleoid observed in the microbodies shows a characteristic morphology which has not been reported before within other plant microbodies. This nucleoid is composed of minute tubular structures, for which the authors here propose a three-dimensional arrangement.     

ROLE OF THE NITROGEN-FIXING BACTERIAL MICROFLORA IN THE EPIPHYTISM OF TILLANDSIA (BROMELIACEAE)

Nitrogen-fixing activity in the phyllosphere of 12 species of Tillandsia from different Mexican habitats was evaluated by the acetylene reduction assay, and nitrogen-fixing microorganisms were isolated and characterized. The leaves from eight of the 12 Tillandsia species examined exhibited nitrogenase activity in enrichment cultures. Among the microorganisms implicated—Agrobacterium, Bacillus, Erwinia, Pseudomonas, Rahnella, Vibrio, and Xanthomonas—only Bacillus megatherium reduced acetylene in pure culture. Our findings suggest that nitrogen fixation in the phyllosphere of the sampled epiphytes occurs under suitable conditions and that most of the bacteria involved are primarily soil and water inhabitants. The results also suggest a relationship between the composition of the nitrogen-fixing microbial communities grown on the leaf and the different development of the leaf area in Tillandsia due to the aerial components (wings) of the trichomes.     

GENETIC VARIATION IN THE EPIPHYTES TILLANDSIA IONANTHA AND T. RECURVATA (BROMELIACEAE)

The genetic structure of two epiphytic species, Tillandsia ionantha and T. recurvata, was investigated using enzyme electrophoresis. Electrophoretic data suggest that T. ionantha and T. recurvata differ in breeding system, in agreement with predictions based on their strikingly different floral morphologies. Electrophoretic data suggest extremely high levels of inbreeding for T. recurvata, whereas Tillandsia ionantha exhibits characteristics of an outcrossing species. Values of P, H, and mean number of alleles per locus are much higher in T. ionantha than in T. recurvata. The mean value of F_IS for T. ionantha is low (0.056), closely approaching expectations at Hardy-Weinberg equilibrium. In contrast, the mean value of F_IS in T. recurvata (1.000) indicates a complete absence of heterozygotes. The two species also differ in genetic structure. Low F_ST values for T. ionantha indicate little variation in allele frequencies among populations. In contrast, F_ST values are high for T. recurvata, suggesting substantial genetic heterogeneity among populations. In addition, the mean value of I is higher in T. ionantha (0.995) than in T. recurvata (0.931). Population genetic data are in agreement with the suggestion of Benzing (1978), who proposed that extreme epiphytes such as T. recurvata, would be characterized by increased autogamy ensuring high seed set. Due to high chromosome numbers in Bromeliaceae (most taxa have x = 25), the family has been considered polyploid. However, with the exception of an additional isozyme for PGM in T. recurvata, the two species are isozymically diploid.     

PLICATE STAMINAL FILAMENTS IN TILLANDSIA SUBGENUS ANOPLOPHYTUM (BROMELIACEAE)

Plication of staminal filaments is an important diagnostic character for Tillandsia subgenus Anoplophytum (ca. 45 species). The monophyletic integrity of subgenus Anoplophytum has recently been questioned, and we conducted an anatomical investigation of plicate staminal filaments to better characterize this putative synapomorphy. Developmental studies show that the filament plications, or folds, become visible during or soon after anthesis. Serial sections of preplication filaments and filaments in sequential stages of plication were prepared and observed with light microscopy. A uniform sequence of parenchyma cell collapse begins three to four cell layers out from the vascular bundle and proceeds centrifugally to the epidermis. Eventually the epidermal cells collapse, leaving only the vascular bundle and a few surrounding parenchyma cells intact. Above and below the zone of plication, all parenchyma and epidermal cells in the filament remain intact. Species traditionally placed in subgenera Tillandsia and Allardtia have been found with plicate staminal filaments that are anatomically and develop-mentally identical to those studied from subgenus Anoplophytum. Alone, staminal filament plication does not appear to be a good diagnostic character for subgenus Anoplophytum, and doubts concerning the monophylesis of this subgenus are reinforced. The functional significance of stamen filament plication remains unknown.     

CLADISTIC TESTS OF HYPOTHESES CONCERNING EVOLUTION OF XEROPHYTES AND MESOPHYTES WITHIN TILLANDSIA SUBG. PHYTARRHIZA (BROMELIACEAE)

Tillandsia L. Subg. Phytarrhiza (Visiani) Baker (Bromeliaceae) is a distinctive group of about 35 epiphytic species. These exhibit a range of habits from xeric to mesic. The evolutionary relationships of the contrasting adaptations need to be established here as well as in the subfamily as a whole. Relations between the subgenus and other tillandsioids are problematical and phylogenetic reconstruction of its member-species would be facilitated by identification of Phytarrhiza's relative (sister taxon) sharing the same most recent common ancestor with Phytarrhiza. This paper examines the two most likely sister taxa, Subg. Pseudo-Catopsis Baker and Subg. Diaphoranthema (Beer) Baker. Diaphoranthema is rejected as sister taxon. The accepted evolutionary tree, rooted by Pseudo-Catopsis, indicates that most habital evolutionary changes in Phytarrhiza have been between mesic and semi-mesic forms and from mesic to xeric forms. Methods developed for testing specific evolutionary hypotheses are broadly applicable.     

OLIGOTROPHIC TILLANDSIA CIRCINNATA SCHLECHT (BROMELIACEAE): AN ASSESSMENT OF ITS PATTERNS OF MINERAL ALLOCATION AND REPRODUCTION

Analyses of Tillandsia circinnata Schlecht specimens from nutrient-stressed and more fertile habitats in southern Florida confirmed earlier findings that its vegetative and reproductive vigor are enhanced as shoot tissue concentrations of P, K and Mg increase. Demands by this perennial herb for N, P and K are more pronounced than for B, Ca, Cu, Fe, Mg, Mn, Mo and Zn, primarily because N, P and K must be maintained at relatively high concentrations in vegetative tissues and are heavily expended during seed production. When most or all of this epiphyte's self-fertile flowers set fruit— a fairly common occurrence in most of the populations examined—asexual propagation by offshoot is subordinated to the sexual effort, especially if the specimen is growing in an unusually sterile habitat and has very limited mineral resources. Predictions implicit in r-K selection and related life history theory are consistent with the notion presented here that T. circinnata is following a pattern of nutrient use for reproductive purposes that represents a highly adaptive way to expend slowly accumulated mineral resources in stressful habitats represented by small, scattered, short-lived microsites. Specifically, it expends scarce mineral resources during the reproductive effort in a way that greatly enhances fecundity and vagility while minimizing the rate at which new microsites and reproducing individuals must be recruited. Reproduction and mineral use by T. circinnata is compared with that of T. utriculata, a semelparous epiphyte that shares many of the same forest habitats in southern Florida.     

DISENTANGLING THE EFFECTS OF KEY INNOVATIONS ON THE DIVERSIFICATION OF BROMELIOIDEAE (BROMELIACEAE)

The evolution of key innovations, novel traits that promote diversification, is often seen as major driver for the unequal distribution of species richness within the tree of life. In this study, we aim to determine the factors underlying the extraordinary radiation of the subfamily Bromelioideae, one of the most diverse clades among the neotropical plant family Bromeliaceae. Based on an extended molecular phylogenetic data set, we examine the effect of two putative key innovations, that is, the Crassulacean acid metabolism (CAM) and the water‐impounding tank, on speciation and extinction rates. To this aim, we develop a novel Bayesian implementation of the phylogenetic comparative method, binary state speciation and extinction, which enables hypotheses testing by Bayes factors and accommodates the uncertainty on model selection by Bayesian model averaging. Both CAM and tank habit were found to correlate with increased net diversification, thus fulfilling the criteria for key innovations. Our analyses further revealed that CAM photosynthesis is correlated with a twofold increase in speciation rate, whereas the evolution of the tank had primarily an effect on extinction rates that were found five times lower in tank‐forming lineages compared to tank‐less clades. These differences are discussed in the light of biogeography, ecology, and past climate change.     

百合花粉母细胞核骨架的超微结构观察

参照动物细胞核骨架的研究方法,用整装电镜技术和DGD包埋-去包埋技术研究了选择性抽提的和完整的百合(Lilium davidii var. willmottiae (Wilson) Roffill)花粉母细胞。结果表明,住减数分裂前期Ⅰ,百合花粉母细胞核内存在一个精细的非染色质纤维——核骨架。该网络由5～15nm的纤维交织而成,广泛地分布于细胞核内。这些核骨架有的分布于染色体间,有的分布于染色体周围,并与染色体和核仁相连。随着减数分裂时间的推移,染色体(质)间核骨架纤维逐渐减少,染色体(质)周围的核骨架纤维逐渐增多,并与染色体内部的纤维结构相连,表明核骨架一方面为染色体拓扑变化提供一个空间支架,另一方面也可能参与了染色体骨架的构建。     

MORPHOLOGICAL CHANGES ACCOMPANYING THE TRANSITION FROM JUVENILE (ATMOSPHERIC) TO ADULT (TANK) FORMS IN THE MEXICAN EPIPHYTE TILLANDSIA DEPPEANA (BROMELIACEAE)

Two distinct morphological forms characterize the ontogenetic development of the epiphytic bromeliad Tillandsia deppeana. Juveniles are characterized by a non-impounding rosette of small, linear leaves covered with elaborate trichomes possessing a 4 + 8 + 16 + 64 shield cell pattern. The broader transitional leaves, which form an impounding rosette prior to the initiation of true adult leaves, also possess trichomes with the 4 + 8 + 16 + 64 cell pattern. Adult individuals have large, broad leaves with overlapping, sheathing bases which impound water and debris. These leaves have trichomes with shields exhibiting a 4 + 8 + 32 cell pattern. Trichome density is fairly uniform in the juvenile leaves with trichomes covering 100% of leaf surfaces, whereas in the adult leaves density is high at the base and diminishes significantly toward the apex. Stomatal density of both juvenile and adult leaves increases from the base to the apex, although this is most pronounced in the adults. Stomata in the adults are also arranged in longitudinal series parallel and abaxial to parallel rows of mesophyll tissue. The results of this study indicate that juveniles of T. deppeana are more similar morphologically to adult atmospheric-type tillandsioid species than to the tank-forming adults into which they eventually develop.     

木兰属几种药用植物花粉粒形态扫描电镜观察

用扫描电镜方法观察木兰属（Ｍａｇｎｏｌｉａ）几种药用植物的花粉粒及花药,其共同形态特征是：花粉粒近球形或长球形,具单沟或不具沟;外壁光滑或较粗糙。花药表皮细胞纺锤形或柱形,排列紧密,具条状纹饰。     

EFFECTS OF SOIL NITROGEN ON POLLEN PRODUCTION,POLLEN GRAIN SIZE,AND POLLEN PERFORMANCE IN CUCURBITA PEPO (CUCURBITACEAE)

To determine the effects of soil nitrogen on pollen production, pollen size, and pollen performance, two cultivars of zucchini (Cucurbita pepo) were grown under two nitrogen regimes in an experimental garden. The two cultivars were true breeding for alternative alleles for a one gene trait, ovary color. The soil nitrogen treatment had a significant effect on most measures of reproductive output through the female function. The nitrogen treatment did not affect the number of staminate flowers per plant but did have an effect on the number of pollen grains per staminate flower and the mean pollen grain size. A pollen mixture experiment revealed that pollen produced by plants in the high nitrogen treatment sired significantly more seeds than pollen from low nitrogen plants. Moreover, we found that the high nitrogen pollen sired even a greater percentage of seeds in the region of the fruit (ovary) previously shown to be fertilized by the fastest growing pollen tubes. Thus, the difference in the number of seeds sired by pollen from the two nitrogen treatments is due to differences in pollen performance. We conclude that spatial heterogeneity in soil nitrogen can influence the paternity of seeds in a plant population.     

THE AURICULATE POLLEN GRAIN OF HYMENOCALLIS QUITOENSIS HERB. (AMARYLLIDACEAE) AND ITS SYSTEMATIC IMPLICATIONS

The pollen grain of Hymenocallis quitoensis Herb, is examined with scanning and transmission electron microscopy. The very large, monosulcate grain is characterized by a coarsely reticulate exine surface and solid, auriculate appendages at the equatorial facies. Surface morphology of the pollen grain of H. quitoensis is compared with other representative species of Hymenocallis and supports the inclusion of H. quitoensis within the genus. Meridional exine dimorphism in other species of Hymenocallis is interpreted as a reduction from the well-defined auriculae of H. quitoensis. Surface morphology of the pollen grain of Hymenocallis sects. Artema Traub and Elisena (Herb.) Traub exhibits divergence from that of sects. Hymenocallis and Ismene (Herb.) Traub. Phylogenetic and paleobotanical implications of the auriculate pollen grain are briefly discussed.     

K-77(2)雄性不育小麦花粉壁结构特征

K-77(2)不育花粉内壁比保持系厚将近一倍。在保持系花粉内壁中,有径向排列的、断断续续的、着色深的管状结构。而不育花粉内壁中则没有管状结构,且在不育花粉内壁中形成许多小泡。在花粉粒后期,往往在Z层与内壁连接处断开。推测,由于花粉内壁结构被破坏,影响了正常的营养运输和萌发所需酶的合成而抑制花粉发育。     

须芒草族植物花粉形态的观察

在光学显微镜下和扫描电镜下对禾本科须芒草族（Ａｎｄｒｏｐｏｇｏｎｅａｅ）中分隶于８个亚族３４个属的３６种植物的花粉进行形态面容和比较研究。结果显示,本族植物花粉形态较为一致,花粉近形或扁球形,单萌发孔,孔,周围加厚,具盖,外壁表面散布有颗粒。这表明其是一个自然类群。总体来讲,芬烨大的演化分异,只是表面纹饰的和芬烨大小有一;定的差异。纹饰可分为三种类型粗糙型,不明显疠状突起才明显疠状突起型。花粉开矿     

利用单花粉蛋白电泳技术对玉米花粉发育过程特异蛋白表达的研究

八十年代,Ｍｕｌｃａｈｙ（１９８１）与Ｃ．Ｇａ６（１９８６）成功地对单个花粉粒同工酶和蛋白质进行了等电聚集电析。而国内在这方面的工作至今尚未见报道。试验利用单花粉蛋白电泳技术结合显微镜观察对不同发育时期的单个玉米花粉进行了蛋白电泳研究,结果表明玉米花粉不同发育时期所表达的蛋白质具有明显的差异：一方面随发育时期的推移某些蛋白质含量呈递减或递增趋势;另一方面不同发育时期都有特异性蛋白合成或分解。可见,     

ULTRASTRUCTURAL OBSERVATIONS ON THE SPERMATOZOA OF PLEUROTOMARIA AFRICANA TOMLIN (GASTROPODA)

Spermatozoa from formalin/alcohol preserved testes of Pleuotomariaafricana Tomlin are examined using transmission electron microscopy.These spermatozoa possess the following features: (1) an acro-somalvesicle (acrosomal cone), 1 µm long and deeply invaginated;(2) an axial rod occupying the inva-gination of the acrosomalvesicle; (3) a cylindrical nucleus (length 4 µm, maximumdiameter 1.5 µm) exhibiting occasional irregular cavities;(4) shallow imaginations at anterior and posterior extremitiesof the nucleus; (5) four or five spherical mitochondria pressedinto posterior indentations of the nucleus, and clustered aroundthe proximal and distal centrioles; (6) a single flagellum continuouswith the distal cen-triole and (7) a satellite fibre—densering complex associated with the distal centriole and attachedflagellum. Substructure of the centrioles could not be determined,but presumably both are composed of triplets. Spermatozoa ofP. africana are simple in structure (as expected of an externallyfertilizing species) and, among the Gastropoda, resemble spermatozoaof some trochids more so than those of other pleurotomaroideans(Haliotidae, Scissurellidae) or the Fissurelloidea. The primitiveposition of the Ple-urotomariidae within the Prosobranchia issupported by sperm morphology ^*Present address: Department of Zoology, University of Queensland,St. Lucia, 4067 Queensland, Australia (Received 30 December 1987; accepted 11 January 1988)