摘要:

Anthopsis deltoidean.gen. et n.sp. of dematiaceous Hyphomycetes, isolated from horticultural soil in Italy, is described. The new fungus is characterized by a peculiar conidial apparatus and by triangular conidia.

ISSN:0008-4026    

DOI:10.1139/b77-018

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The productivity ofPotamogeton Richardsonii, P. pectinatus, Myriophyllum alterniflorum, Megalodonta Beckii, andChara vulgarisin West Blue Lake, Manitoba, is reported. Measurements of changes in biomass and assimilation of14CO2in random and non-random samples throughout the growing season of 1973 were used. Changes in biomass ofP. Richardsonii, M. alterniflorum, M. Beckii, andC. vulgarisdetermined from random samples compared favourably with those determined from non-random samples. This was not the case forP. pectinatusbecause of its restricted occurrence. Similarly, measurements of14CO2assimilation in random samples ofP. Richardsonii, M. alterniflorum, andM. Beckiicompared well with non-random samples. Productivity values derived from14CO2uptake were far in excess of those attained from biomass changes. Seasonal trends of production and the depth distribution of production are discussed, and macrophyte production is compared with phytoplankton production.

ISSN:0008-4026    

DOI:10.1139/b77-019

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Unicellular or uniseriate trichomes with helical outer wall bands were found in several taxa of Rosaceae, Betulaceae, and Rubiaceae during a survey of cleared and stained leaves of 93 species in 86 genera of 52 families. Outer wall bands were most common in Rosaceae, especiallyRubus. Previously, only bands on the inner wall of trichomes had been described. Trichomes with outer wall bands may provide excellent material for basic cell wall studies, and in certain families they may be a useful taxonomic character.

ISSN:0008-4026    

DOI:10.1139/b77-020

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Swellings were consistently observed in the glume axils of young differentiating inflorescences of 22 taxa of the subtribe Triticinae. The swellings arose from cell divisions in the tunica (surface and subsurface) and outer cortex (underlying) layers, indicating that they were floret primordia, but since further development was arrested, they are termed latent floret primordia. Occasional floret development in the glume axils has been reported by others. The primordia were present in axils of both glumes in apical spikelets, but only in the second glume of lateral spikelets. They were rapidly obscured by developing glumes, and in lateral spikelets were more easily viewed from the abaxial (inner) side. Because of the ubiquity of the characteristic, it is proposed to be of ancient origin, and possibly can be exploited to increase the grain number and yield of wheats.

ISSN:0008-4026    

DOI:10.1139/b77-021

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

When sunflowers are infected by the vascular pathogenVerticillium dahliae, the first visible foliar symptom is the appearance of tiny chlorotic flecks. An attempt was made to determine the temporal order in which early ultrastructural changes leading to symptom expression occur. The evidence indicates that ultrastructural changes occur in the following order: (1) degradation of xylem vessel walls, (2) initiation of the necrotic band, (3) degeneration of the mesophyll tissue remote from the vein, and (4) degeneration of the phloem. The possible importance of xylem vessel plugs and of phenolic compounds to the initiation of symptom development is also discussed.

ISSN:0008-4026    

DOI:10.1139/b77-022

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Soybeans with mature plant resistance and a nonhost, string bean, were inoculated withPeronospora manshurica. Soybeans resistant, susceptible, and intermediate in reaction were inoculated for comparison. Leaves were fixed, cleared, and stained, and whole mounts were made daily. Individual infection sites were examined, and hyphae were measured microscopically. Spore germination varied as a result of self-inhibitory factors. Where it occurred, entrance by the fungus appeared identical on each plant at 12 h. Hyphal growth became rapid in susceptible tissue 36 h after inoculation; growth slowed, starting at 72 h in mature tissue, and was uniformly slow in tissue intermediate in resistance. Hyphal growth after 36 h was essentially zero in resistant tissue, but paradoxically it was sometimes rapid on nonhost tissue. Haustoria occurred in all plants inoculated. The number of haustoria per lesion increased in proportion to the length of hyphae, except on resistant tissue, where the number of haustoria per millimetre of hyphae was very low.

ISSN:0008-4026    

DOI:10.1139/b77-023

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Using systematical as well as stratified sampling, the authors discussed the phytosociological organization of a 10-km-long by 150-m-wide system of mobile dunes in the Magdalen Islands. They recognized a marked toposequence from the shoreline toward the interior, including nine phytosociological elements, for the most part found in parallel zones. In this paper, they discuss the aerial and underground vertical stratification, the plant composition, and the ecological distribution of those elements.

ISSN:0008-4026    

DOI:10.1139/b77-024

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The Red Lake Peatland, situated on the eastern arm of the Lake Agassiz plain in north central Minnesota, is made up of large black spruce raised bogs separated by sedge-covered water tracks marked by string patterns and teardrop-shaped forested islands. About 3 m of peat overlie a prairie soil; the basal peat is 3170 ± 100 years old (14C date). Stratigraphic distribution of pollen, macrofossils, and peat components in a series of cores along a small forested island was used to study the development of the peatland.In pollen zone RLB-1 (lowest) the upland pollen types suggest an oak savanna with a developing mesic deciduous forest. The local pollen indicates a succession from aTyphamarsh to a sedge meadow. Zone 2 shows a small rise inPinuspollen; Ericaceae pollen andSphagnumspores indicate the development of a bog–heath vegetation type at the coring site. An increase in pollen of spruce and larch reflects the establishment of the island forest. Zone 3 is marked by a rise inAmbrosiapollen, recording agricultural land clearance in northwestern Minnesota in about 1890.TheSalix–herb macrofossil assemblage occurs at the base of some cores; it is succeeded stratigraphically by theTypha–Scirpusassemblage, which also makes up the base of the remaining cores. There follows theCarex diandra–Carex aquatilisassemblage, suggesting a sedge meadow. The overlyingMenyanthes–Larixassemblage continues to the surface under the sedge fen; under the island, seeds ofChamaedaphneand needles ofPiceaoccur in this assemblage. The incoming of theMenyanthes–Larixassemblage is believed to reflect the first development of the patterned wetland.Reed peat comprises the bottom 20–50 cm of all cores; it corresponds with the lower part of pollen zone 1 and contains theTypha–Scirpusmacrofossil assemblage. Pure sedge peat or sedge peat with Bryales corresponds with zone 2 and upper zone 1 of the pollen diagram and contains theCarex diandra–C. aquatilismacrofossil assemblage. Ericaceous peat occurs only under the island, and it contains theMenyanthes–Larixmacrofossil assemblage. Laterally under the present sedge fen it grades into sedge peat with ericaceous components.The general upward succession of communities observed in these peat cores can be duplicated along a west-to-east surface traverse across the present prairie–forest transition. The stratigraphic succession thus records the westward movement of the prairie–forest transition across Beltrami County about 4000–2000 years ago.The area was covered by prairie more than 3100 years ago. Development of a cooler, moister climate led to aTyphamarsh in the poorly drained lowland; oak savanna occupied the surrounding upland. As the water level rose in the lowland, peat started to accumulate as sedge meadow developed, and aspen parkland and conifer–hardwood forest moved into the upland. About 2000 years ago the growth ofSphagnummoss increased, accompanied by the development of patterned wetland and bog forest, with conifer–hardwood forest on the upland.

ISSN:0008-4026    

DOI:10.1139/b77-025

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The effects of daily pretreatment with low levels of ozone (0.02 μl litre−1) on the susceptibility of primary bean leaves to acute ozone injury involve several stages. Plants subjected daily to low ozone from the time of sowing exhibit an early resistance to acute injury which decreases with time. When the low ozone pretreatments begin about 10 days after sowing, there is no change in susceptibility for 2–3 days, then it increases to a level which remains constant. At the start of this period of greater susceptibility, such pretreated plants are more susceptible than controls in filtered air; after about 8 days, they are less susceptible because of the marked increase insusceptibility of the controls with time. In contrast, daily pretreatments with higher (0.05 μl litre−1) levels, beginning 8 days after sowing, cause an initial decrease in susceptibility followed by a marked increase, leading to predisposition to acute injury.The early increase in susceptibility of plants transferred from filtered air to 0.02 μl ozone litre−1appears to be the result of the decreased ability of stomates to close in response to high ozone levels. The later stage of decreased relative susceptibility is associated with a dampening of stomatal activity, which is independent of the presence of high ozone levels.

ISSN:0008-4026    

DOI:10.1139/b77-026

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The host–parasite interaction betweenPhysalospora obtusaand the biotrophic contact mycoparasiteCalcarisporium parasiticumwas studied by light and electron microscopy. After hyphal contact between the two fungi, a contact cell was delimited by a septum in the germ tube apex ofC. parasiticum. Subsequently, a portion of the appressed walls of the host–parasite interface was dissolved, creating a large pore through which cytoplasmic exchange occurred. The results of this study explain, in part, how increased nutrient uptake from the host by the parasite is accomplished and dispells the hypothesis that the contact cell increases the permeability of the host plasmalemma to nutrients and required growth factors.

ISSN:0008-4026    

DOI:10.1139/b77-027

出版商:NRC Research Press    

年代:1977

数据来源: NRC