摘要:

A comprehensive review of the mosses of Labrador is presented, incorporating all previously published reports and much new data accumulated during field and herbarium studies since 1970. A total of 348 species of mosses are documented for Labrador, of which 40 are new to that region.Grimmia atratais new to North America, and a major southern range extension is reported forOligotrichum falcatum. Four species of 'copper mosses' occur together at Nachvak, northern Labrador. Illustrations ofMielichhoferia elongataand a large falcate form ofM. mielichhoferiare presented, with comments on differentiating the two species. A preliminary bryogeographical analysis indicates that at least 75 moss species of southern affinity have their northern limit for eastern North America in Labrador, and a smaller number of predominantly arctic moss species have southern limits in Labrador.

ISSN:0008-4026    

DOI:10.1139/b78-056

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Cell division inMarehantia polymorphaandM. berteroanawas examined with the electron microscope. Distinct preprophase bands of microtubules, typical of higher plants, were not observed. Most of the spindle microtubules in early prophase appeared to insert into polar MTOC's. The behaviour of the nuclear envelope, nucleolus, and chromosomes was typical of higher plant divisions. Cytokinesis was accomplished by centrifugal cell plate growth in a phragmoplast. Numerous coated vesicles were associated with the developing cell plate.

ISSN:0008-4026    

DOI:10.1139/b78-057

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Growth and xylem differentiation in cotyledonary shoots were studied by partially isolating one shoot surgically in nondecapitated and decapitated flax plants (Linum usitatissimumvar.noralta). Three types of cuts were made. The first type separated the shoot from the hypocotyl and the second from the epicotyl. The third type of cut was made at the node separating the two shoots, which, however, remained independently connected with the hypocotyl and epicotyl. In nondecapitated plants, the lateral shoots were inhibited. They had at their bases primary xylem strands, some of which were connected with the hypocotylary stele; the strands contained predominantly tracheids. In decapitated plants, the separated shoot grew vigorously when it was connected with both hypocotyl and epicotyl or hypocotyl alone. Such shoots contained at their bases abundant secondary xylem strands which were connected with the hypocotylary stele; the strands included predominantly vessels. The shoot that was isolated from the hypocotyl but connected with the epicotyl was inhibited even though it had abundant secondary xylem strands at its base. Results of this study suggest that growth of the cotyledonary shoot is dependent on the prior development of adequate xylem connections with the hypocotylary stele.

ISSN:0008-4026    

DOI:10.1139/b78-058

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The endosperm of the African blood lilyHaemanthus KatherinaeBak. follows the helobial pattern of development in which two chambers of endosperm are formed. In the earliest observed stage of development a large micropylar chamber and a smaller dome-shaped chalazal chamber of endosperm are present. Both are coenocytic and contain wall ingrowths of the transfer cell type along the embryo sac wall. Freely growing walls grow centripetally from the embryo sac wall, branch, and eventually meet, forming a layer of cells along the embryo sac wall. This process occurs first in the micropylar chamber. After four or more layers of endosperm cells are present, phragmoplasts form in association with karyokinesis and give rise to cross walls situated between the freely growing walls. When 10 or more layers of endosperm cells are present, free wall-less cells are present in the central vacuole near the edge of the cellular endosperm of the micropylar chamber. The free cells originate from mitosis of nuclei at the inner wall-less edge of the endosperm and the subsequent pinching off and release of the free cells into the large central vacuole. The free cells may undergo karyokinesis and become binucleate. The chalazal chamber of endosperm also becomes cellular by means of freely growing walls.

ISSN:0008-4026    

DOI:10.1139/b78-059

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Correlated fluorescence, bright-field, transmission electron, and scanning electron microscopic studies were made on developing root nodules ofComptonia peregrina(L.) Coult. (Myricaceae) produced by a soil actinomycete which invades the root and establishes a symbiosis leading to fixation of atmospheric dinitrogen. After entering the host via a root hair infection, the hyphae of the endophyte perforate root cortical cells by local degradation of host cell walls and penetration of the host cytoplasm. The intracellular hyphae are always surrounded by host plasma membrane and a thick polysaccharide material termed the capsule. (For convenience, term intracellular refers to the endophyte being inside aComptoniacell as distinguished from being intercellular, i.e.. between host cells, even though the former is actually extracellular as the endophyte is separated from the host cytoplasm by the host plasmalemma.) Numerous profiles of vesiculate rough endoplasmic reticulum (RER) occur near the growing hyphae. Although the capsule shows a positive Thiery reaction indicating its polysaccharide nature, the fibrillar contents of the RER do not, leaving uncertain whether the capsule results from polymers derived from the RER. Amyloplasts of the cortical cells lose their starch deposits during hyphal proliferation. The hyphae branch extensively in specific layers of the cortex, penetrating much of the host cytoplasm. At this stage, hyphal ends become swollen and form septate club-shaped vesicles within the periphery of the host cells. Lipid-like inclusions and Thiery-positive particles, possibly glycogen, are observed in the hyphae at this time. Associated with hyphal development is an increase in average host cell volume, although nuclear volume appears to remain constant. Concomitant with vesicle maturation, the mitochondrial population increases sharply, suggesting a possible relationship to vesicle function. The intimate interactions between host and endophyte during development of the symbiotic relationship are emphasized throughout.

ISSN:0008-4026    

DOI:10.1139/b78-060

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Various Lower Tertiary epiphyllous microfungi are described from southern Australia, including the monotypic new genusCribrites aureaand the new speciesCallimothallus australis. Modern equivalents were searched for in 72 leaf-litter samples from Australasia. The habitat indicator value of the fossils is assessed by comparison with the geographic, climatic, and vegetational relationships of the modern forms.

ISSN:0008-4026    

DOI:10.1139/b78-061

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

An apparatus and a method for centrifuging living, inoculated plant tissues were developed for studies of a cytoplasm-related host response of barley coleoptiles to penetration by the powdery mildew fungusErysiphe graminis hordei. When the coleoptiles were attached to the apparatus with the long axes of the cells parallel to the centrifugal force, cytoplasm-rich and cytoplasm-poor zones were produced, permitting simultaneous comparisons of interactions in the presence or absence of host cytoplasm. The inner epidermis was inoculated and centrifuged for 12–14 h at 4750 × g. Desiccation was prevented by addition of liquids at the cut end of each coleoptile; the rest of the coleoptile was dry and suitable for inoculation withE. graminisconidia. Of the host cells, 50–80% had well-compacted cytoplasm, conidia developed penetration and infection structures, and the host response was restricted to cytoplasm-rich zones and was shown to be cytoplasm-dependent. Cytoplasmic streaming resumed within 10 min after centrifugation stopped, and 90–100% of the epidermal cells were actively streaming 3 h later. This centrifugation method could be adapted and applied to studies of the other host–parasite interactions.

ISSN:0008-4026    

DOI:10.1139/b78-062

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Exposure to full sun provided the most stressful environment, as reflected by foliar characteristics, for naturally occurringRhododendron macrophyllumgrowing at low to middle elevations. However, for a given age, exposed plants had a greater woody biomass than shaded plants. In comparison with shaded plants, foliar chemical concentrations (as percentage dry weight) were greatly reduced, unit-area concentrations were greatly increased, total leaf area per plant was reduced about half, and average leaf areas and specific blade areas were greatly reduced. Exposed plants also lacked almost totally the normal fourth age class of foliage.Reduced temperatures and growing-season length, associated with shaded sites at high elevation, caused intermediate levels of stress. This was indicated by intermediate unit-area measurements of foliar chemical concentrations, total leaf area per plant, average leaf size, and specific blade area. Percentage dry weight concentrations did not differ significantly from those of other shaded plants. Foliar biomass per plant was similar for the high-elevation site and the exposed site. Woody biomass of shaded plants at high elevations was similar to that of shaded plants at low elevations.Results showed that the dimensional characteristics of leaves (average leaf area, specific blade area), the total leaf area per plant, and foliar chemical concentrations expressed on a unit-area basis were the foliar characteristics most accurately reflecting stressful environments.

ISSN:0008-4026    

DOI:10.1139/b78-063

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Vegetative shoot tips of mature western red cedar (Thuja plicataDonn) were cultured on defined nutrient media. In the presence of high concentrations of various gibberellins, microsporangiate strobili were induced from the vegetative tips during an 8-week period under continuous illumination. No strobili were induced by GA3under short-day (SD; 8-h photoperiod) conditions or continuous darkness. The ontogenetic stages of strobilus induction and development in culture were similar to those reported for intact plants. Prolonged culture produced externally mature male strobili. However, histological examination of the sporogenous tissues revealed either abortion of the tissues or an apparent arrest in early meiosis. Wide concentration ranges of either IAA or NAA in the presence or absence of 1 × 10−4 MGA3did not qualitatively modify the early development of male strobili or induce female strobili, although 1 × 10−4MIAA completely inhibited induction of the male strobili by GA3. Benzylaminopurine or kinetin suppressed the induction of male strobili by GA3, while Ethrel or abscisic acid at the concentrations tested had no apparent qualitative effects on microsporangiate strobili formation.

ISSN:0008-4026    

DOI:10.1139/b78-064

出版商:NRC Research Press    

年代:1978

数据来源: NRC