摘要:

The VAM mycorrhizal status of five plant species growing in a serpentine soil in which a notable concentration of toxic elements such as nickel, cobalt, and chromium is present was assessed using standard techniques. The root systems of all plant species examined were colonized by VAM fungi, with the exception of the typical serpentinophyteAlyssum bertoloniibelonging to theCruciferae. Using the «inoculated pot cultures» technique, we identified four species ofGlomus, described a fifth, and observed two species ofSclerocystis.

ISSN:0017-0070    

DOI:10.1080/11263508909430241

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Calluna vulgaris(L.) Hull possesses a root system with fine rootlets, usually called «hair roots». Longitudinal median sections of growing hair roots show the presence of an apical meristem consisting of separate initials (specific initials for central cylinder and cortex, a common initial for epidermal and cap cells organized as a dermatocalyptrogen) and a simple differentiated zone. The general histological organization is characteristic of Dicotyledons, even though the reduced number of initials and the total size of the hair root lead to a «miniaturized» root. The differentiated zone lacks root hairs and the cortical cells quickly collapse before vascularization takes place. Some ultrastructural features of cellular differentation are noteworthy: nuclear changes, versatility of dictyosomes, production of mucilage, and deposition of tannins in the epidermal and cortical cells.

ISSN:0017-0070    

DOI:10.1080/11263508909430242

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Species ofFusariumSection Gibbosum, isolated from onion seed, are identified asF. equiseti, F. compactumandF. acuminatum. Some features of conida on CLA and aspects and growth rates of colonies on PDA are briefly recorded. In addition to CLA, a simple method based on the use of cellulose was helpful in some identifications.

ISSN:0017-0070    

DOI:10.1080/11263508909430243

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Fertilization and seed development were studied inCrocus sativusL., after pollination withCrocus thomasiiTen. Fertilization was porogamous and resulted in the formation of zygote and primary endosperm nucleus; it was accompanied by degeneration of the receptive synergid and followed by degeneration of the antipodals. The endosperm developed precociously by free nuclear division, occuping a parietal position; subsequently it filled the central vacuole and became cellularized. The zygote divided after a quiescence period by formation of a transversal wall; its division was accompanied by degeneration of the persistent synergid. The embryo developed from the apical cell and, at maturity, was a cylindrical structure showing histological differentiation of the shoot apex. The seed coat was formed from both integuments. Both embryogeny and development of the endosperm and seed coat were entirely similar to those ofCrocus thomasii.

ISSN:0017-0070    

DOI:10.1080/11263508909430244

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

This paper deals with the ovule and anther structure, sporogenesis, and gametogenesis ofAnreda cordifolia(Ten.) Steenis. The conclusions are: the anther wall develops according to the Monocotyledonous type of Davis(1966). The tapetum is secretory and the endothecial cells develop U-form thickenings on radial and internal tangential walls. Microspore mother cells undergo simultaneous cytokinesis and the microspore tetrads are tetrahedral. Pollen grains are 3-celled when shed. At anthesis the ovule is orthoamphitropous crassinucellar and bitegmic with the micropyle formed by the inner integument. The archesporial cell cuts off a primary parietal cell which becomes the parietal tissue. A nucellar cap develops from the nucellar epidermis. The outer integument is dermal and subdermal in origin but the inner is only dermal. Only one archesporial cell differentiates from the nucellus, and the megaspores are arranged in T-tedrads. The chalazal megaspore produces an 8-nucleate embryo sac which develops according to thePolygonumtype. The mature synergids present a filiform apparatus that accords to the type. I following Cocucci(1981). The antipodal cells are ephemeral. Starch grains accumulate in the synergids, egg cell and central cell. Finally, the systematic value for Basellaceae of the embryological characters here considered, is discussed.

ISSN:0017-0070    

DOI:10.1080/11263508909430245

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A small species ofPolysiphoniaGreville collected in the northern Thyrrenian Sea is described. Specimens have been tentatively referred toPolysiphonia pseudovillum, species unknown from the Mediterranean Sea, on the basis of the correspondence existing between their morphological and taxonomical characters. The importance of some of these characters for the identification of MediterraneanPolysiphoniaspecies is also emphasized.

ISSN:0017-0070    

DOI:10.1080/11263508909430246

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Graft experiments betweenAcetabularia acetabulumL. (Silva) andBatophora oerstediiJ. Agardh have shown that incompatibility exists between these two Dasycladaceae. The grafted nucleated basal fragments ofAcetabulariadie or eventually regenerate a new cell. The enucleated halves ofBatophorasurvive for more than 3 months and develop numerous sporangia which remain sterile.

ISSN:0017-0070    

DOI:10.1080/11263508909430247

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Population demography and dynamics of the genus Verbascum in an abanddoned field (Central Apennin, Italy). - Four populations of the genusVerbascumin a recently abandoned field were examined. A demographic inventory of the species was made along two transects in each 2x2 m quadrat. Results show thatV. thapsusandV. lychnitis, which largely dominated the other ones, are in a regression phase; colonization began thanks to the contribution of seeds from the road-side populations. The different models of diffusion and the number of generations involved are described for both species. The distance covered byV. thapsusduring the three generation expansion leads to the hypothesis of a seed-dispersal range larger than the literature reports. The subsequent season only a very small population ofV. lychnitissurvived, confirming the predictive analysis of life-structure.

ISSN:0017-0070    

DOI:10.1080/11263508909430248

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Time and space in ecological studies on vegetation dynamics. Considerations on the significance of time and space in ecological studies on vegetation dynamics may concern three groups of problems philosophical-methodological, organisational-methodological and cognitive.

ISSN:0017-0070    

DOI:10.1080/11263508909430249

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0017-0070    

DOI:10.1080/11263508909430250

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor