摘要:

The examination of the seed coat ofCucurbita maximawith the scanning electron microscope provided information about the three-dimensional structure of the seed coat cells. The lumpy appearance of the spongy parenchyma cells indicated that localized wall growth must have occurred. Also of particular interest were the reticulate secondary wall thickenings in the hypodermal and spongy parenchyma regions of the seed coat. The developing squash seed coat may prove to be a good model system in which to study the cell wall deposition process.

ISSN:0008-4026    

DOI:10.1139/b73-221

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Descriptions, illustrations, and distribution data are given for three closely related species ofAtriplexnative to North America. Most populations ofAtriplex subspicata(Nutt.) Rydberg are hexaploid, with a chromosome count of 2n = 54. Two populations were found with counts of 2n = 36.Atriplex gmeliniiC. A. Meyer andA. alaskensisS. Watson are hexaploids.Atriplex subspicatahas been confused by North American botanists withA. patulaL. andA. hastataL. but these introduced species are respectively tetraploid and diploid.

ISSN:0008-4026    

DOI:10.1139/b73-222

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

The growth response ofFusarium solanito benomyl or thiabendazole in the medium was found to differ from that of many otherFusariumspecies tested. In contrast to the steep, linear dosage–response curve typical for this genus, the curve forF. solaniinvariably reaches a maximum at about 1.0 μg/ml and is horizontal from there on. During a single exposure to either benomyl or thiabendazole,F. solanidevelops tolerance to both toxicants, but its subsequent growth on untreated medium is retarded. Cross-tolerance to other benzimidazoles is also induced. Such adapted strains generally maintain their slow growth habit and tolerance indefinitely through successive transfers to either untreated or treated medium. Occasionally a colony growing slowly on untreated medium will produce a sector which grows normally but proves to be sensitive when transferred to treated medium. Conversely, colonies of this sensitive strain, while growing extremely slowly on treated medium, more frequently produce a sector like the resistant strain. From observation of the response of a large number of single-spore isolates it is concluded that in the presence of a benzimidazole a high proportion of the wild population can mutate to the slow-growing, resistant type. Such mutants occasionally revert to the wild type.

ISSN:0008-4026    

DOI:10.1139/b73-223

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

An increasing sugar gradient in the rib, a decreasing gradient in the upper region of the petiole, and a sharp increase in the base of the petiole were found when transverse segments of the rib and petiole of a sugar beet leaf or the isolated vascular bundles as a whole were analyzed. The sugar concentration and the gradient pattern varied considerably with the leaf position in the ontogenic sequence. The proportion of assimilated14C exported as sucrose was highest for leaves of intermediate age, which were at the nearly mature stage. Mature and old leaves exported less14C and young leaves, which had a high sugar concentration in the blade and a sharply decreasing gradient in the petiole, exported very little. Analysis of vascular bundles in the petiole which serve the tip and basal regions of the blade after14CO2incorporation into the blade indicated that a much larger amount of14C-sucrose entered into and moved through the basal bundle than into and through the tip bundle.

ISSN:0008-4026    

DOI:10.1139/b73-224

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Twenty-one additional species new or rare to Nova Scotia are reported. Of these, 12 belong to the Rhodophyceae, 6 to the Phaeophyceae, 1 to the Chlorophyceae, and 2 to the Xanthophyceae.Acrochaetium porphyraeandScytosiphon dotyi, two species previously known only from the west coast of North America, are recorded for the first time from the Atlantic coast of that continent.Porphyrodiscus simulonsandEntonema polycladum, known from Europe, are also recorded for the first time in North America.

ISSN:0008-4026    

DOI:10.1139/b73-225

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Conioscypha lignicolaHöhnel andC. variaShearer were studied with the electron microscope. Conidiogenesis appears to be intermediate between annellidic and phialidic. Single conidia are produced endogenously by a percurrently proliferating conidiogenous cell. The wall of the conidium initial and its basal septum do not participate in the structure of the conidium.

ISSN:0008-4026    

DOI:10.1139/b73-226

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Sporophytic chromosome numbers were determined for 216 species, varieties, or hybrids of the genusHaworthia. There were 152 diploids (2n = 14), 10 triploids, 38 tetraploids, 7 pentaploids, 7 hexaploids, and 2 aneuploids. Among the species studied, most of the diploids were highly fertile. The tetraploids were somewhat less so, the triploids were generally less than 50% fertile, and the pentaploids and hexaploids were generally intermediate between the diploids and the triploids. The few diploid interspecific hybrids were less fertile than the diploid species. Each additional set of chromosomes increased the pollen size, and this increment was found to be significant up to the tetraploid level. Statistical analyses of comparisons between pollen size means of the hexaploids and pentaploids, and of the pentaploids and tetraploids were not significant. Pollen sterility is interesting in connection with the problem of speciation in the Aloineae, which is discussed.

ISSN:0008-4026    

DOI:10.1139/b73-227

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Seed of the American highbush cranberry,Viburnum trilobumMarsh., kept at germinative conditions of 20 °C, required 328 days to reach 92% germination. Initially, about one-half the seed germinated within 120 days. After a 120-day lag, the balance germinated. Afterripening, with as little as one cycle of alternating temperature (1 week at 20 °C and 1 week at 2 °C) shortened the time to total germination bymonths. The inductive effect of afterripening was studied in relation to utilization of the high lipid reserve present in the endosperm. No appreciable changes in polar and non-polar lipids occurred during prolonged exposure to either afterripening or germinative conditions, indicating that afterripening is not associated with lipid degradation. Gibberellic acid (GA3) had little effect on seed germination but successfully overcame epicotyl dormancy of the seedling.

ISSN:0008-4026    

DOI:10.1139/b73-228

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Several features of the concept of floristic zonation, as a special case of biogeographical zonation in general, are examined. A distinction between description and hypothesis testing provides a preliminary systematization of methods used to detect the presence of zonation by analysis of distribution records. It is argued that the use of range limits largely fails to take the statistical nature of distribution records into account. Accordingly, three ordinational methods which do not depend upon range limits are applied to presence–absence data for 100 species of vascular plants occurring in southern Ontario. Two of these methods, canonical correlation and principal-components analysis, explore the idea that linear combinations of differential weightings upon the members of a set of taxa may demonstrate clearer geographical trends than merely treating all taxa as equally important trend-setters. The results of the study appear to bear this out. No sharply demarcated zonal boundaries emerged from the analyses, but two of the methods indicated the presence of weakly developed tension zones which may be taken as evidence of floristic zonation in southern Ontario.

ISSN:0008-4026    

DOI:10.1139/b73-229

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Light-inhibited spore germination inBotrychium dissectumformaobliquumoccurred in axenic culture on a nutrient medium containing 0.25% sucrose. The spores had to be cultured in darkness for 3–4 weeks before any germination would take place. Longer periods in the dark produced greater percentages of germination. Sucrose was unnecessary for germination, but it promoted gametophytic growth once germination had occurred.

ISSN:0008-4026    

DOI:10.1139/b73-230

出版商:NRC Research Press    

年代:1973

数据来源: NRC