摘要:

The presence of specific P-type sieve-element plastids is reported for 16 and betalains for 14 species of Portulacaceae. The micromorphology of sieve-element plastids and the presence of betalains support a closer relationship of the Portulacaceae to the Aizoaceae than to the Caryophyllaceae. Three genera,Ceraria,Portulacaria, andTalinella, previously treated as doubtful members of the Portulacaceae, cannot be distinguished from members of the Basellaceae on the basis of plastid subtypes since the two families have identical subtypes; however, the data do confirm their alignment with the Portulacaceae–Basellaceae family group.

ISSN:0008-4026    

DOI:10.1139/b75-236

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The phenomenon of self-parasitism in the aquatic phycomycetes has apparently been overlooked since it was first mentioned in the work of Klebs in 1899. This study documents fungal self-parasitism for the first time inSaprolegnia megaspermaCoker (isolate 369A). The 369A isolate was grown for 48 h at 16 °C in shake cultures of a medium containing glucose, lactalbumin hydrolysate, phosphate, and micronutrients. The resulting vegetative growth was then transferred to shake-and-standing flasks at 16 °C and standing flasks at 4 °C containing either a dilute salts solution or double-distilled water to enhance the formation of both sexual and asexual structures. The results in both shake and standing cultures were comparable. When oogonia were produced in the absence of antheridial branches, the oospheres developed into normal oospores. When an antheridial branch was produced, an antheridial cell was never observed and the branch penetrated the oogonium via a pit and destroyed all or some of the oospheres (oospores?). This parasitic antheridial branch could reemerge from an oogonium via a pit and penetrate additional oogonia. The possible implications of self-parasitism for the relationship betweenS.megaspermaandSaprolegnia unispora(Coker and Couch) Seymour are discussed.

ISSN:0008-4026    

DOI:10.1139/b75-237

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Evolutionary relationships amongAvenaspecies were inferred by means of computer cladistic analysis. The method of Farris for computing Wagner networks was applied separately to the diploid and to the hexaploid species. The method of Camin and Sokal was applied to the diploid species only. A great number of networks were generated of which representatives are documented in this paper. After various roots have been chosen, a number of trees thus determined are proposed as hypotheses of cladistic relationships. Unit character consistencies were also computed to assess the degree of homoplasy of the characters in the different trees.

ISSN:0008-4026    

DOI:10.1139/b75-238

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The effects of increasing concentrations of heavy water (2H2O) on the growth, development, morphology, and transpiration patterns inNicotiana tabacumL. were studied throughout the life cycle of the plant. The higher deuterium levels caused a marked reduction in size and flowering, together with extensive tissue necrosis. These observations are consistent with the literature on the effects of deuterium on plant development. The present study showed a deleterious effect of deuterium on alkaloid production, associated with heightened transpiration rates and decreased fractionation of carbon isotopes in photosynthesis. All of the observed effects are consistent with the established view of deuterium as a nonspecific chaotropic agent, whose effects are evident at every level of plant organization.

ISSN:0008-4026    

DOI:10.1139/b75-239

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Ultrastructure of the macroconidia ofFusarium solanias visualized by transmission (ultrathin sectioning and freeze-etching) and scanning electron microscopy is described. The cell wall has four layers. The innermost layer is electron-lucid followed by an electron-dense layer. The next outer layer is spongy in appearance followed by a superficial layer consisting of fine filamentous processes. Freeze-etch replicas of conidia directly removed from the sporodochia and still suspended in the mucilaginous material (in which they are produced) frequently show the conidia connected by the superficial filamentous processes in the cell wall. This agglutination of the conidia is likely to increase the inoculum potential of this pathogen at the sites of infection. Structure of various membrane systems in the cells is described. The endoplasmic reticulum is fairly extensive and fenestrated. Thin sections of routinely fixed conidia show myelin figures. However, such structures were not seen in replicas of conidia that were freeze-etched without use of chemical fixation or cryoprotection.

ISSN:0008-4026    

DOI:10.1139/b75-240

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Recently published fossil dinoflagellate taxa of and below the generic rank and not included in the authors'Fossil Dinoflagellates: Index to Genera and Species(published in 1973) are listed alphabetically. The dinoflagellates are classified as plants, so their taxonomy is governed by the provisions of the International Code of Botanical Nomenclature.

ISSN:0008-4026    

DOI:10.1139/b75-241

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The moss flora of the northern lowlands of Devon Island (75°33′ N, 84°40′ W) is reported to consist of 131 species and 2 varieties. Forty-five of these are reported as new to the island.Sphagnum orientaleL. Savicz. is reported as new to North America andPlagiobryum zierii(Hedw.) Lindb. andPolytrichum algidumHag. & C. Jens, are reported as new to the Queen Elizabeth Islands.A key is given to the species and varieties, which is followed by a discussion of critical taxonomic and ecologic criteria for each species.

ISSN:0008-4026    

DOI:10.1139/b75-242

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Soluble carbohydrate patterns of two hardy winter wheat cultivars and two less hardy cultivars were compared during the cold-hardening process. Soluble carbohydrates increased in concentration as the seedlings developed and the cold-hardening process occurred. The largest soluble carbohydrate differentials between the hardy and less hardy winter wheat cultivars occurred in the sucrose and raffinose fractions. The accumulation of sucrose and raffinose in wheat growing at 7.2 °C–0.5 °C day–night was greater in the two less hardy winter wheat cultivars. An inverse relationship existed between soluble sugars and cold hardiness in the four cultivars studied.

ISSN:0008-4026    

DOI:10.1139/b75-243

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Observations have been made on the anatomy of beech,Fagus grandifoliaEhrh., with an emphasis on quantitative features. All surface areas and volumes were determined by projecting 2-μm serial sections, measuring them with a map tracer, and multiplying cell perimeters by section thickness or by the trace–cut–weight method. The organization of tissues, including a complex reticulate venation, is typical of many dicotyledons. Of the minor veins, only the quinternaries and veinlets lack bundle sheath extensions and have wholly parenchymatous bundle sheaths, the cells of which are often oriented at right angles to the vein. There are 12.1 mm of vein per square millimetre of leaf surface area, and 10 μm of vein (the diameter of a mesophyll cell) serves about 21.5 mesophyll cells. The mean maximum distance over which water and solutes must move between vascular tissue and mesophyll is 55 μm. The mesophyll cell walls may provide the pathway through which the bulk of the water moves; the volume occupied by the mesophyll cell walls is 55.7 mm3or 11% of total leaf volume. The evaporative surface of the mesophyll is 13.36 mm2/mm2leaf surface area.

ISSN:0008-4026    

DOI:10.1139/b75-244

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The small (about 2 × 3.5 μm) zoospore of the obligately parasitic chytridRozella allomycisprovides yet another ultrastructural variation on the basic pattern of posteriorly uniflagellate fungal zoospores. This zoospore contains the expected array of organelles: nucleus, mitochondria, "lipid sac" (including lipid globules, a microbody, and a backing membrane), kinetosome, and second centriole. Ribosomes are dispersed throughout the cytoplasm. In the disposition of its microbodyRozellaresembles other chytrids, whereas in the occurrence and location of its gamma-like vacuoles it resembles certain blastocladialean fungi. Above all, the zoospore resembles that ofOlpidium brassicae. Structural peculiarities of the zoospore include (i) bilateral symmetry; (ii) a helmet-shaped nucleus with extensive membranous projections which surmounts a large, spheroidal mitochondrion; and (iii) a particularly elongate cell shape because of the unusual length (about 1 μm) of the kinetosome and the presence of a 1-μm-long flagellar cavity which surrounds the base of the flagellum. Cytoskeletal elements include cytoplasmic microtubules, microfilaments which mainly reinforce the flagellar cavity, and props which anchor the kinetosome in the plasmalemma at the roof of the flagellar cavity. The role of these elements is discussed. A revision of the description of the olpidiaceous zoospore is suggested.

ISSN:0008-4026    

DOI:10.1139/b75-245

出版商:NRC Research Press    

年代:1975

数据来源: NRC