摘要:

Nine North American species ofPohlia, sectionPohliella, form a complex of morphologically and ecologically similar species. In western North America, where there is a broad region of overlap in geographic ranges, they frequently grow together in various combinations. Over 300 soil samples representative of these species were analyzed with respect to organic matter content, pH, and concentrations of exchangeable calcium and magnesium ions, and each species was found to be distinctive in terms of these environmental factors. Morphologically variable species tend to be ecologically and geographically widespread, while less variable species tend to be more restricted. Species with a predominance of primitive morphological features occur primarily on tundra soils of intermediate pH, while morphologically advanced species inhabit road banks or other disturbed sites where the pH may be high or low.

ISSN:0008-4026    

DOI:10.1139/b81-290

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Anatomically preserved vegetative remains ofMetasequoia milleriRothwell and Basinger are common in the Princeton chert of the Allenby Formation in southern British Columbia. Deposition of the Allenby Formation and associated volcanics occurred during Middle Eocene time. The Princeton chert locality is in the upper strata of the Allenby Formation and is of late Middle Eocene age. The Princeton chert was formed by siliceous permineralization of marsh soil. Dissolved silicates were probably introduced by periodic influx of water from mineral springs or geysers.Anatomical features of stems, wood, and leaves are well preserved. Mature wood of the fossil resembles that ofMetasequoia glyptostroboidesin having traumatic resin cysts; opposite pitting on radial walls of tracheids; taxodioid cross-field pitting; tall, uniseriate rays; smooth-walled ray parenchyma; and diffuse, resinous, smooth-walled wood parenchyma. Leaves are linear, hypostomatic, and borne decussately, and have one or three resin ducts and slightly undulate to smooth epidermal cell walls. Leaves of livingM.glyptostroboidesdiffer in consistently having three resin ducts and much more pronounced undulations of epidermal cell walls.Metasequoia millerihas leaves of a generalized structure from which leaf types of many taxodiaceous genera could be derived. Roots associated withM.milleriare dimorphic. Primary tissues and secondary phloem are exceedingly well preserved. Cortex of both long and short roots contains mycorrhizal fungi.Compression remains ofM.occidentalisare not distinguishable fromM.glyptostroboides. Anatomical features ofM.milleri, however, do reveal differences between Eocene and livingMetasequoia. Wood rays ofM.milleriare much higher than those ofM.glyptostroboides. Other features of stem anatomy are similar in both species. Pollen cones differ in developmental and minor anatomical features. The close similarity of most organs ofM.milleritoM.glyptostroboidesand the dissimilarity of leaf structure indicate mosaic evolution within the genus.

ISSN:0008-4026    

DOI:10.1139/b81-291

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Modified vessel wall layers and their ultrastructural characteristics in branches of artificially inoculated elm (Ulmus americanaL.) trees surviving the acute disease stage and of naturally infected, chronically diseased trees are described. Walls of large early-wood vessels in zones where disease action was prevalent have a strong stain reaction and may be uniformly or locally three to four times thicker than normal.In smaller vessels (some including vessel tracheids), an extra lignified-like, often discontinuous layer may be present. This layer is generally demarcated from the normal by a dense band. Pit membranes and vessel end plates are likewise much thickened through the presence of an opaque material similar to that of the pit membrane. This material differs from that forming the coating layer which like tyloses is generally present inside the thickened or extra vessel wall layer.The possible significance of these observations, particularly in relation to disease development and tree resistance, is discussed.

ISSN:0008-4026    

DOI:10.1139/b81-292

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Various ultrastructural cell wall modifications of fibres have been observed in artificially or naturally infected American elm (Ulmus americanaL.) trees surviving the acute stage of the Dutch elm disease caused byCeratocystis ulmi(Buism.) C. Moreau. Bands of fibres with gelatinous (SG) layers characteristic of tension wood are frequent in or near invaded tissues; similar layers are also present sometimes in cells identifiable as parenchyma. The SG layer is often different from that observed in healthy trees. Masses or bands of dense material are present which often extend perpendicular as tubular structures to the plasmalemma location. Also, orientation of fibrils in such layers may be disordinate. One or more additional lignified-like layers alternating with additional SG-like or other opaque layers may occur inside the first SG layer. The innermost layer in these cases is often lamellate.Small intracellular locules delimited by one or two wall layers also occur in other cells.The possible significance of these observations in host–parasite relationships of the disease is briefly discussed.

ISSN:0008-4026    

DOI:10.1139/b81-293

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Tracer exported from wheat and maize leaves after photosynthetic fixation was resolved into theoretical pools by mathematical analysis of the rate of loss of either14C or11C from the leaf. Fusicoccin, known to stimulate the proton–sucrose symport, had no effect on the rate constants of exchange between pools or loading into the translocation stream of normal plants. K+-deficient plants showed an increased transfer of C into the storage pool when treated with fusicoccin. Parachloromercurobenzylsulphonic acid known to inhibit export not only reduced the rate constant for export but also increased the exchange from the export pool to the storage pool.

ISSN:0008-4026    

DOI:10.1139/b81-294

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Root segments obtained from field-grown corn plants were divided into small sections and assayed for acetylene (C2H2) reduction. After overnight preincubation, C2H2reduction started immediately and linear rates were observed for several hours. Addition of NO3−(1 mM) delayed the start of C2H2reduction but linear rates followed thereafter. A similar pattern was observed with excised roots inoculated withAzospirillum lipoferum.Addition of malate did not eliminate the NO3−effect. Inoculation withA.lipoferumresulted in relatively large rates of C2H2reduction and a shorter lag than normal (4 to 8 h). A transient accumulation of NO2−accompanied the disappearance of NO3−and C2H2reduction started only after all the NO2−had been reduced. A very sizable fraction of the reduced NO3−and NO2−was accounted for as N2O accumulation. Thus, the results provided support for thein situoperation of both N2fixation and denitrification inA.lipoferum– corn root associations and it is proposed that mature corn roots are able to provide sufficient carbon to support both processes.

ISSN:0008-4026    

DOI:10.1139/b81-295

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The relationship ofExobasidium(Exobasidiales) to other groups of Basidiomycetes has long been questioned. Although this genus has been traditionally placed in the Holobasidiomycetes, septal ultrastructure, combined with other features of the basidium, suggest a much closer relationship to the Teliomycetes.

ISSN:0008-4026    

DOI:10.1139/b81-296

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Pure culture isolates were obtained from fungi fruiting in the vicinity of dwarf willows at Barrow and Cape Simpson, Alaska. Four of these isolates and one isolate from Maryland were tested for their ability to form ectomycorrhizae with cuttings ofSalix rotundifoliaunder controlled environmental conditions. Isolates ofEntoloma sericeum,Hebelomapusillum, andCenococcum geophilumfrom Barrow and Cape Simpson, Alaska all formed typical ectomycorrhizae withS.rotundifolia, while an isolate ofC.geophilumfrom a temperate ecosystem (Maryland) did not.All of the ectomycorrhizae synthesized withS.rotundifolia, plus uncolonized roots, demonstrated an ability to hydrolyzep-nitrophenyl phosphate at a pH of 4.7. The acid phosphatase activity ofE.sericeumectomycorrhizae was from 10 to 40 times as great as that demonstrated by other mycorrhizal and nonmycorrhizal roots on a surface area basis.

ISSN:0008-4026    

DOI:10.1139/b81-297

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The host–parasite relations of an insect–fungus blister gall onSolidago graminifoliaand a related gall onS.rugosawere studied. The midge,Asteromyia carbonifera, and fungus,Sclerotium asteris, were associated with both gall types.Externally, young galls of both types had a black center surrounded by a yellow halo. During growth in diameter the external coloration did not change inS.graminifolia; however, inS.rugosaa beige – ashy grey area developed in the center of the black region and expanded outward. In both species the leading edge of intercellular fungal hyphae was present in the halo region. Behind this front, hyphae sequestered to form an undifferentiated subepidermal stroma. The stroma differentiated into a black cortex and underlying white medulla at the margin of the black region. Differentiated cells remained subepidermal in both species except for the cortex that became subcuticular inS.graminifolia. During cortical proliferation inS.graminifoliathe cuticle remained intact; however, epidermal cells became isolated and collapsed. InS.rugosathe epidermis separated extensively from the mesophyll but remained intact. Mesophyll cells within the halo and black region exhibited a reduction in number and size of chloroplasts and starch grains in both species.

ISSN:0008-4026    

DOI:10.1139/b81-298

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The release of rhizobia from infection threads of mung bean (Vigna radiata) root nodules is an endocytotic process. The peribacteroid membrane surrounding the released bacteria is initially derived from the host plasma membrane which surrounds the infection thread and not from the nuclear envelope as previously reported by Prasad and De. Endoplasmic reticulum (ER) profiles and Golgi vesicles fuse with the infection thread cell wall and adjacent host plasma membrane. Although some ER profiles were continuous with the outer membrane of the nuclear envelope, no continuities of the nuclear envelope with the infection thread, the host plasma membrane, or the peribacteroid membrane were observed. Furthermore, no blebbing of the nuclear envelope was observed.

ISSN:0008-4026    

DOI:10.1139/b81-299

出版商:NRC Research Press    

年代:1981

数据来源: NRC