摘要:

The flagellar apparatus is described in zoospores of Rhizophydinm chlorogonii,R. constantineani, R. haynaldii, R. laterale, R. patellarium. R. pollinis-pini, R. sphaerotheca, R. subangulosnm, Phlyctochytrium plurigibbosum, Chytridium confervae, C. olla, C. lagenaria, Rhizoclosmatium globosum, andRluzophlyctis rosea, which are all members of the order Chytridiales. In fine structure, the flagellar apparatus is basically similar to that of fungi in other orders of the class Chytridiomycetes. The characteristics of the flagellar apparatus which are unique to the class are: (1) kinetosome props and associated segment of doublets with a curved extension seen as a hook in thin sections; (2) a spiral structure which connects to the A tubules of the doublets and coils in the core of the transition zone. These characteristics distinguish this class of fungi from the Oomycetes, from algae, protozoa, and other eukaryotes. It is further proposed that six modifications to the flagellar apparatus within the Chytridiales are diagnostic characteristics which could be used for describing subgroupings within the order. These modifications are the presence of a fibrous rhizoplast in some species; presence and form of electron-dense inclusions in the basal area; arrangement of kinetosome-associated microtubules; presence of an electron-dense area in the base of the flagellum; the angle of the nonfunctional centriole to the kinetosome and the presence of a veil-like structure on the side of the nonfunctional centriole. Taxonomic implications of these findings are discussed.

ISSN:0008-4026    

DOI:10.1139/b78-102

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Thirty-seven species of the generaAegilops, Agropyron, Elymus, Eremopyrum, Haynaldia, Hordeum, Secale, andTaeniatherumin the tribe Triticeae and six species of the genusLoliumin the tribe Festuceae were tested for their reaction to loose smut of barley,Ustilago nuda, and loose smut of wheat,U. tritici. One new host forU. nudawas found:Hordeum violaceum. Fifteen new hosts forU. triticiwere found:Aegilops caudata, Ae. ovata, Ae. triuncialis, Agropyron caninum. A. fibrosum, A. scabrifolium, Elymus canadensis, E. dahuricus, E. virginicus. Haynaldia villosa, Hordeum brachyantherum, H. jubatum, H. marinum, Secale silvestre, andTaeniathernm crinitum. Six new hosts for bothU. nudaandU. triticiwere found and they are the first known common hosts for these fungi:Agropyron scabriglume. A. striatum, A. tsukushiensevar.transiens, Hordeum bogdanii, H. brevisubulatum, andH. compressum. On all these hosts, the sori ofU. nudawere covered by a thin membrane or peridium whereas the sori ofU. triticiwere naked. Spores formed on all hosts germinated in the manner typical for the species used for inoculation. The wild barley common in Canada.Hordeum jubatum, differentiated between races of loose smut of wheat,U. tritici. Six species ofLoliumwere resistant toU. nudaandU. tritici.

ISSN:0008-4026    

DOI:10.1139/b78-103

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The taxonomy of this western European, maritime, cliff-inhabiting species complex has in recent years been based primarily on chemistry. Five of the species are characterized by a replacement series of medullary depsidones and a sixth is acid deficient. The taxonomy of this group has been reinvestigated using modern methods of thin-layer chromatography and numerical taxonomy based on individuals collected from three well separated regions in western Britain.The discovery that low concentrations of protocetraric acid usually accompany salazinic acid leads to the supposition that it may be a precursor compound in the same way that norstictic acid is widely accepted as being the precursor of stictic acid. The chemical structures of the compounds also support such a view. In addition, hypoprotocetraric acid is structurally very similar to protocetraric acid so that two biosynthetic pathways can be hypothesized for the group. These are as follows: (1) hypoprotocetraric → protocetraric → salazinic acid and (2) norstictic → stictic acid.Three types of numerical classification were undertaken to test for the presence of a correlation between morphological attributes (39) and chemical attributes (variable numbers). These are classifications in which (1) chemical attributes were excluded. (2) medullary constituents were given equal weight, and (3) putative biosynthetic pathways were given greater weight than their constituent substances. The three methods each produced two virtually identical clusters corresponding to individuals possessing one or other of the two biosynthetic pathways, a result which established a close correlation between morphology and chemistry within the group. Cophenetic correlation coefficients between the classifications were in excess ofr = 0.900. Acid-deficient individuals were found associated with both clusters.Comparison of the within- and between-group sums of squares showed that the two clusters represent taxa which in view of the strong correlation between morphology and biosynthetic pathways, should be recognized at the species level. Principal components analysis of a data set derived from that used in type 3 classification also produced the same two clusters. This analysis also yielded two subgroups within each cluster which are to be the subject of further studies. The correct names for the two species corresponding to individuals with the salazinic and stictic acid pathways areRamalina siliquosa(Huds.) A.L.Sm. andR. cuspidata(Ach.) Nyl., respectively.

ISSN:0008-4026    

DOI:10.1139/b78-104

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The two species are shown to be almost perfectly sympatric, but their centres of abundance on the shore are different,Ramalina cuspidatabeing most abundant low in the supralittoral andR. siliquosamost abundant higher in this zone. Principal component analyses show that the within-species variation, which is considerable, is continuous in both species. Correlation of the attribute scores and height above sea level of the individuals with the component scores for the individuals demonstrates that inR. cuspidataboth morphological and chemical variation are related to vertical position on the shore. Only chemistry is related to vertical position inR. siliquosa, morphological variation being controlled by angle of rock surface and protection from inundation. The continuum of morphological variation is considered to be a response to a potential evapotranspiration gradient in both species. Individual ramuli ofR. cuspidatafrequently exhibit a wide range of the morphological continuum along their length indicating that morphological variation is not the result of genotype selection. There is no unequivocal evidence by which to refute the widely held view that the zonation of chemotypes in both species is the result of habitat selection. However, it now seems more probable that chemical variation may be explained as being the result of progressive truncation of biosynthetic pathways as a response to an increasingly stressful environment with increasing height above sea level. The concept of morphological buffering is introduced and the role of morphological plasticity in the survival strategy of lichens is discussed.

ISSN:0008-4026    

DOI:10.1139/b78-105

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

In a 20-year-old abandoned surface coal-mining area in eastern Ohio, fiber-glass litterbags containing thalli of two cryptogam species and leaves of 10 dominant tree species were set out in four vegetated stands influenced to varying degrees by the impact of strip mining. Decomposition rate of the litter types studied was correlated with the soluble carbohydrate, ash, and macronutrient fractions of the litter. No effects of strip mining on litter decomposition were apparent in any of the vegetated stands.Metal elements (Mn, Fe, Al, Cu, Zn, and Mo) were found to accumulate in decomposing litter with time. The degree to which dominant metals (Mn, Fe, and Al) were lost or accumulated with time was significantly correlated with the initial metal content of litter, indicating that a cation-exchange process is probably involved in observed metal-mobilization patterns.Leaching experiments using distilled water acidified to pH5.5 with H2SO4to simulate rainfall in this region revealed that litter types which exhibited generally high decomposition rates or high initial amounts of metals tended to lose metal elements as a result of leaching. Metal-mobilization patterns evident from the litter-decomposition experiment indicated that the 1st month of litter decomposition results in metal loss owing to leaching.

ISSN:0008-4026    

DOI:10.1139/b78-106

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Three types of rod-shaped viruslike particles (VLPs) (a short rigid rod (RR), 260 × 12 nm. a long narrow-diameter flexuous rod (NFR), 660 × 10 nm, and a long wide-diameter flexuous rod (WFR), 740 × 16 nm) and a spherical VLP (35 nm in diameter) were found in extracts of uredospores, germ tubes, and pustules of cowpea rust, negatively stained with ammonium molybdate. Both the size distributions and the stability of these VLPs was affected by the choice of stain since when phosphotungstic acid was used, two additional length classes of the RR (150 nm and 90 nm) were noted, and this stain tended to disassemble the WFR by unwinding the helix of this particle. The WFR also disassembled at pHs 4and5 in 10 mMacetate but only at pH 4 in the presence of 0.2 MNaCl. Examination of cowpea rust by thin sectioning revealed the presence of four types of VLPs. Morphologies of these particle types were consistent with the data obtained by negative staining.

ISSN:0008-4026    

DOI:10.1139/b78-107

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Pollen size and aperture number are reported for nine North American species ofMyriophyllum. For seven of these, scanning electron micrographs are provided. The wall sculpture ofM. alterniflorumis microrugulate and that of eight other species is microverrucate. InM. exalbescensandM. tenellum, microvermcae develop late in pollen maturation.Myriophyllum farwellii, a species that flowers underwater, has asymmetrically arranged pores and variation in pore number. An estimated 90% ofM. farwelliipollen, from collections made in 1975 and 1976, had collapsed: the apparently sterile grains suggest that this species is at least partly apomictic. A pollen key to the species is provided.

ISSN:0008-4026    

DOI:10.1139/b78-108

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The total area and number of xylem rays and vessels from tangential and cross sections of twigs of 12 sugar maples (Acer saccharumMarsh.) were determined by the use of an image-analyzing computer. A nested analysis of variance indicated that xylem rays of trees of high sap and sugar yield are more numerous and larger than the rays of other sugar maples. The total area and number of xylem vessels were about the same in all 12 trees.

ISSN:0008-4026    

DOI:10.1139/b78-109

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The initiation of callus and tracheids from lettuce pith explants is inhibited when initial ethylene levels are above 100 nl/ℓ. When initial ethylene levels were near 2 nl/ℓ, lettuce pith explants cultured in small continuously sealed vials demonstrated no reduction in callus development compared with controls, but unlike the controls, they demonstrated no tracheid development. An hypothesis is advanced that ethylene has little effect on cell division per se, but at concentrations in excess of 100 nl/ℓ, it may inhibit the cytodifferentiative events leading to callus production and (or) tracheid development in lettuce pith exp

ISSN:0008-4026    

DOI:10.1139/b78-110

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Seasonal fluctuations of the epipelon in five eutrophic, prairie–parkland lakes were characterized by spring and late summer – autumn maxima, although midsummer peaks, dominated by chlorococcalean algae, occurred at the shallow stations in three lakes. Winter peaks were invariably dominated by algae of planktonic origin. The epipelon was light limited at the deep stations under ice cover during the winter. More correspondence than in previous studies was found between the standing crop and the nutrient status of the overlying water but no one single factor could account for seasonal fluctuations of the epipelon. Instead, a combination of light levels, nutrients, temperature, physical disturbance, and biotic interactions affected these fluctuations. The mean standing crop size of the epipelon was closely related to the mean bicarbonate levels.

ISSN:0008-4026    

DOI:10.1139/b78-111

出版商:NRC Research Press    

年代:1978

数据来源: NRC