青麸杨分泌道的解剖学研究

报道了育麸杨分泌道的结构、分布和发育。青麸杨的分泌道是由14—41个分泌细胞围绕细胞间隙而成的腔道,分泌细胞外侧又被多层扁平的鞘细胞所包围。青麸杨的分泌道主要分布于根、茎、叶、花和果实的维管束的韧皮部内,此外,茎的髓中也有少量分泌道,分泌道位于木质部脊处的薄壁组织内,排列成一圈。青麸杨各器官中的分泌道的发生方式一致,都是裂生方式起源的。     

管花肉苁蓉茎异常结构的发育解剖学研究

管花肉苁蓉茎内存在类似于单子叶植物的散生初生维管束。它由散生在基本分生组织中的原形成层束分化而成。在原形成层来分化的过程中,每个原形成层束可通过分离形成2—7个初生维管束,使初生维管束的数目迅速增加。当初生维管束开始正常次生生长时,正常维管束韧皮部外方的薄壁组织细胞或远离维管柬的薄壁组织细胞转变为异常形成层束。异常次生维管束与正常维管束以韧皮部相对或韧皮部并列的方式排列,或异常次生维管束单个存在于薄壁组织中。     

Gibberellin-ethylene interaction controls radial expansion in citrus roots

The involvement of gibberellins (GAs) and ethylene in the process of root radial expansion was studied in young seedlings of Carrizo citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.]. The GA inhibitors cycocel, paclobutrazol, and tetcyclacis enhanced radial expansion of the root tip (up to 2.3-fold) as a result of increases in stele diameter and inner cortex width. The GA deficiency increased cell number and width, and changed the polarity of growth, generating wider and shorter cortical cells in the elongation zone. In the presence or absence of GA inhibitors, GA₃ decreased root tip width and reduced all parameters related to radial expansion. The ethylene inhibitors (aminooxyacetic acid; cobalt ions, CoCl₂; silver thiosulfate) suppressed swelling induced by GA deficiency, generating thinner cells just as GA₃ did. In contrast to GA₃, ethylene inhibitors produced longer cells strongly resembling those of the untreated seedlings. Ethylene released by ethephon did not modify root tip width in control plants, while root diameter behind the root tip was increased. In the presence of low and ineffective concentrations of cycocel, the ethylene precursor 1-aminocyclopropane-1-carboxylic acid increased radial expansion of root tips (1.3-fold) and changed the polarity of growth, producing wider and shorter inner cortical cells as GA inhibitors did. These observations imply, first, that ethylene is the hormonal effector of the process of root radial expansion and, second, that the endogenous GAs modulate the promotive response of ethylene. Received: 4 October 1996 / Accepted: 25 December 1996     

Stem xylem features in three Quercus (Fagaceae) species along a climatic gradient in NE Spain

 Stem xylem features in two evergreen Quercus species (Q. coccifera and Q. ilex) and a deciduous one (Q. faginea) were analysed along an Atlantic-Mediterranean climatic gradient in which rainfall and winter cold experience strong variation. Mean maximum vessel diameter, vessel density, vessel element length, xylem transverse sectional area, Huber value (xylem transverse sectional area per leaf area unit), theoretical leaf specific conductivity (estimated hydraulic conductance per leaf area unit) and total leaf area were determined in 3-year-old branches. Q. faginea presented the widest vessels and the highest theoretical leaf specific conductivity while Q. coccifera showed the lowest total leaf area and the highest Huber value. Studied features did not exhibit significant correlations with mean minimum January temperature in any species but did show significant relationships with rainfall. In Q. coccifera, mean maximum vessel diameter, vessel element length and theoretical leaf specific conductivity increased with higher rainfall while vessel density decreased. Mean maximum vessel diameter and total leaf area in Q. ilex increased with precipitation whereas variables of Q. faginea did not show any significant trend. Results suggest that aridity, rather than minimum winter temperature, controls stem xylem responses in the studied evergreen species. Q. faginea traits did not show any response to precipitation, probably because this species develops deep roots, which in turn makes edaphic and topographic factors more important in the control of soil water availability. In response to aridity Q. coccifera only exhibits adjustment at a xylem level by reducing its water transport capacity through a reduction of vessel diameter without changing the amount of xylem tissue or foliage, whereas Q. ilex adjusts its water transport capacity in parallel to the foliage area. Received: 13 January 1997 / Accepted: 8 April 1997     

From epiphyte to tree: differences in leaf structure and leaf water relations associated with the transition in growth form in eight species of hemiepiphytes

Stranglers must undergo a transformation in growth form from epiphyte to tree to become reproductive mature and thus require developmental and/or physiological plasticity to cope with radical changes in their rooting environment. Differences in leaf structure and water relations between epiphytic-phase and free-standing individuals were marked in the five Ficus species examined. Epiphytic Ficus had several-fold higher specific leaf area (cm₂ g^?1) and 2- to 4-fold lower stomatal densities than conspecific trees. Osmotic potentials at full saturation were, on average, 0-6 MPa higher (less negative) and the bulk modulus of elasticity approximately 50% lower in epiphytic plants than in conspecific trees. This resulted in leaves of epiphytic and tree individuals losing turgor at approximately the same relative water content, hut at a substantially higher leaf water potential in the epiphytic plants. In contrast, differences in leaf structure and water relations between epiphytes and trees of Clusia minor and Coussapoa villosa were small. In greenhouse experiments, alteration of the water and nutrient supply to epiphytic F. tuerckheimmii plants did not lead to significant changes in leaf structure.     

黄芪性状特征与物种及土壤条件相关性研究

黄芪的性状特征目前仍然是衡量根质量的一项重要指标,它们可因物种及生长的土壤条件而有所不同。作者研究了膜荚黄芪（Ａｓｔｒａｇａｌｕｓｍｅｍｂｒａｎａｃｅｕｓ（Ｆｉｓｃｈ．）Ｂｇｅ．）和内蒙黄芪（Ａｓｔｒａ－ｇａｌｕｓｍｏｎｇｈｏｌｉｃｕｓＢｇｅ．）的生长环境和染色体组型,土壤类型和根系形态的相关性,根的解剖学和根的柴性的相关性。研究结果表明,黄芪根系形态与物种,土壤类型有密切的关系。从根的解剖学上论证了黄芪根的绵性与韧皮纤维,柴性与木纤维数量有直接关系,为优质黄芪栽培技术提供了理论依据     

The flora of the early Miocene Brandon Lignite, Vermont, USA. VIII. Caldesia (Alismataceae)

Caldesia, a genus of aquatic monocotyledons, is represented by four living species, which are widely distributed in the temperate and tropical Old World. The genus has an extensive Oligocene through Pleistocene fossil record in Eurasia. We survey the morphology of the extant and fossil fruits of the Alismataceae, and provide a detailed review of the morphology and anatomy of living and fossil Caldesia fruits. The latter exhibit substantial similarity, making the recognition of separate species on the basis of fruit morphology difficult. We erect the new species Caldesia brandoniana from the Early Miocene Brandon Lignite of Vermont primarily on the basis of its geographic isolation; careful revision of all fossil fruiting material of Caldesia might require placement of the Brandon specimens in a more inclusive form species. Together with leaves of Caldesia from the Miocene Clarkia flora of Idaho, this occurrence indicates that Caldesia was in the New World as recently as the Early Miocene.     

Polygyrid relations: a phylogenetic analysis of 17 subfamilies of land snails (Mollusca: Gastropoda: Stylommatophora)

The family of polygyrid land snails in North America is significant for its sympatric shell convergences, diversity of mating systems and complex zoogeography; its monophyly and its relation to other families has long been questionable. Cladistic analysis has been performed on one representative each of 17 subfamilies, including all three polygyrid subfamilies and one or more subfamilies each from all ten of the families that have been proposed as the polygyrid sister groups. Eighteen anatomical synapomorphies are used, of which eight are newly discovered, four are differently assessed from previous studies, and six are traditional. The resulting strict consensus tree of alternative maximum-parsimony cladograms is: (Acavidae (Ammonitellidae Corillidae ((Discidae Oreohelicidae) (Helminthoglyptidae Bradybaenidae Polygyridae (Thysanophoridae (Camaenidae Sagdidae)))))).
According to this working hypothesis, the Polygyridae are monophyletic, and their sister group remains unresolved, although the Acavidae, Ammonitellidae, Corillidae, Discidae and Oreohelicidae can be ruled out. Of the five classifications of stylommatophoran families that have been proposed in the past 12 years, the consensus tree is closest to that of Nordsieck. For future morphological work, three regions are recommended as potentially rich in unused phylogenetic information: the fertilization pouch-seminal receptacle complex, the ureter at the pneumostome and the ventral-chain ganglia. Simultaneous dissection, wkh side-by-side comparisons, is recommended over other methods for detecting homologies in land snails. Molecular characters should be exploited, because of the scarcity and the frequent homoplasy of morphological characters.     

Water-stress-induced xylem embolism in three species of conifers

Abstract. The mechanism of water-stress-induced xylem embolism was studied in three species of conifers: Abies balsamea (L.) Mill., Picca rubens Sarg, and Juniperus virginiana L. Each species showed a characteristic relationship between xylem tension and the loss of hydraulic conductivity by air embolism. Abics balsamea and Picca rubens began to embolize at tensions between 2 and 3 MPa and were completely non-conducting between 3 and 4 MPa. Juniperus virginiana was least vulnerable, beginning to embolize at 4 and still retaining approximately 10% conductivity at 10 MPa. As with a previous study of the vessel-bearing Accr saccharum Marsh., a brief perfusion of branch segments with an oxalic acid and calcium solution (10 and 0.1 mol m⁻³. respectively) increased the vulnerability of the xylem to embolism; this was especially pronounced in Abies balsamea . In order to test whether embolism was caused by aspiration of air into functional tracheids from neighbouring embolized, ones (the 'air-seeding'hypothesis), hydrated branch segments were injected with air at various pressures and measured for embolism. Results supported the air-seeding hypothesis because the relationship between injection pressure and embolism for both native and oxalic-calcium-treated segments was essentially the same as for embolism induced by xylem tension. Structural and experimental evidence suggested the air seeding occurred through inter-tracheid pit membranes when the thickened torus region of the membrane became displaced from its normal sealing position over the pit aperture. Thus, the embolism-inducing tension may be a function of pit membrane flexibility. This tension is of ecological significance because it reflects to some extent the range of xylem tensions to which a species is adapted.     

THE RED ALGAL EPIPHYTES MICROCLADIA COULTERI AND M. CALIFORNICA (RHODOPHYCEAE,CERAMIACEAE). II. BASIPHYTE SPECIFICITY1

The phenomenon of basiphyte specificity in the settlement and growth of the red algal epiphytes Microcladia californica Farl. and M. coulteri Harv. was examined by studying the interface with their respective basiphytes and by cross-inoculation experiments. Microcladia californica attaches only to the surface of its single basiphyte Egregia menziesii (Aresch.) Turn. whereas M. coulteri penetrates the tissue of a wide range of basiphytes. The pattern of primary rhizoid development in both epiphytes determines the mode of attachment and may influence the range of basiphytes possible for each epiphyte. Cross-inoculation experiments show that Microcladia californica is not able to colonize the basiphytes of M. coulteri, Iridaea and Prionitis, or Ulva. The mechanisms by which these algae restrict the growth of epiphytes include short life-span, “cuticle peeling” and chemical defense. Microcladia coulteri, which naturally colonizes Iridaea and Prionitis, has evolved mechanisms to counteract the antifouling effects of those basiphytes. The question of why Egregia is the exclusive substratum for M. californica remains undetermined. However, Egregia may provide the appropriate ecological conditions and a surface topography conductive to M. californica spore settlement and growth.