摘要:

A correlated light and electron microscope study of the root cap of the fernOphioglossumshows that a central and peripheral region can be distinguished. Central cells develop large distally displaced amyloplasts, somewhat thickened cell walls with plasmodesmata mainly in the transverse walls, vacuoles (many of which contain dense osmiophilic inclusions), and proximally located endoplasmic reticulum. Young peripheral cells have randomly located amyloplasts, vacuoles (some of which contain osmiophilic deposits), and rather uniformly and slightly thickened cell walls with a few plasmodesmata. With age, the peripheral cells undergo many changes including a loss of starch and the appearance of many plastoglobuli in the plastids, a thickening of cell walls (particularly on the outer tangential wall), and an eventual breakdown of the cytoplasm. During wall thickening, dictyosomes which pinch off two types of vesicles, electron-dense vesicles and those containing fibrillar material, are abundant in the cytoplasm. Both types of vesicles fuse with the plasmalemma and apparently release their contents into the wall. The root apical cell and its immediate derivatives are characterized by a large nucleus, plastids with small starch grains, many small vacuoles mostly containing dense osmiophilic deposits, and a cell wall with a large number of plasmodesmata.

ISSN:0008-4026    

DOI:10.1139/b77-215

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Twenty different chytridiomycetes were isolated from a small sphagnum bog in northern Michigan. Three of these are considered to be new, namely.Rhizophydium porosumn.sp.,R. undulatumn.sp., andPhlyctochytrium incrustansn.sp. The identity of several are left in doubt, in particular one tentatively assigned toCatenaria sphaerocarpa.

ISSN:0008-4026    

DOI:10.1139/b77-216

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Roots of the garden peaPisam sativumL. cv. Little Marvel inoculated withRhizobium leguminosarumstrain 1019 produce small white nodules which are ineffective in fixing atmospheric nitrogen. Analyses of cytokinin contents of the nodules at different ages using extraction, purification, and thin-layer chromatographic separation showed that the cytokinins zeatin and zeatin riboside and isopentenyladenine and its riboside were present in greatest amounts early in nodule development and decreased thereafter. A new unidentified cytokinin was present in older nodules. The early stages of the infection process in the ineffective nodules were similar to those observed in effective nodules. However, bacteria released from the bacterial thread via an unwalled droplet were not always surrounded by a host membrane. In later stages of nodule development many infected cells contained rhizobia with no enclosing membranes so that the bacteria were free within the host cytoplasm. Such cells showed very low frequencies of mitochondria, of polyribosomes, and endoplasmic reticulum. Thus, the biosynthetic capacity of the cells appeared to be impaired and membrane synthesis defective. The failure of the nodules to develop nitrogenase activity is probably related to the failure of membrane formation around the bacteria. Abnormalities in amyloplast formation were also noted, as well as structural differences in the nodule, including a higher proportion of uninfected cells and earlier cessation of mitotic activity in the nodule meristem than occurs in effective nodules of pea. Transfer cells were observed in the pericycle in both effective and ineffective nodules.

ISSN:0008-4026    

DOI:10.1139/b77-217

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Ascospore germination ofSporormiella intermedia, S. isomera, andS. minimarequires sodium acetate as an exogenous source of energy. Maximum ascospore germination occurs at a concentration of 5.0 g/ℓ of sodium acetate in the medium. Among the physical factors studied, the pH of the medium was found to be crucial: germination occurred within a very narrow pH range (5.0–7.0) and reached an optimal level at pH 5.5. The ascospores ofS. intermediaandS. isomeragerminated between 10 and 30 °C while those ofS. minimagerminated between 10 and 40 °C. The optimal temperature varied for each species (10–20 °C forS. intermedia; 20–25 °C forS. isomera; 30–35 °C forS. minima). At 30 °C and above, a globose vesicle formed in all three species before the formation of the germ tube. Light had no influence on ascospore germination, nor were external supplies of nitrogen or vitamins necessary for spore germinatio

ISSN:0008-4026    

DOI:10.1139/b77-218

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Three species ofSporormiella(S. intermedia, S. isomera, andS. minima) grew and fruited over wide ranges of pH and temperature. The optimum pH was 7.0 or above and the optimum temperature range forS. intermediaandS. isomerawas between 15 and 25 °C and forS. minimabetween 15 and 35 °C. Light did not affect either growth or fruiting. Ammonium acetate,D-alanine, andL-proline were excellent nitrogen sources for growth and fruiting. Several of the best utilized carbon sources were the following carbohydrates: monosaccharides:D(+)-xylose,D-glucose, fructose, andD-mannose; disaccharides:D(+)-cellobiose and maltose; polysaccharides: Alphacel, dextrin, and starch; sugar alcohols: mannitol and sorbitol. Growth increased linearly with an increase in the concentration of carbon from 1 to 8.0 g/ℓ. Sucrose was poorly utilized byS. intermediaandS. minimawhileS. isomerafailed to utilize it entirely. None of the species studied utilized lactose. Alphacel yielded (at all concentrations) the maximum number of ascocarps. In the case of the other carbohydrates,S. intermediaandS. isomeraproduced the maximum number of ascocarps at very low concentrations of carbon (1.0 g/ℓ). Maximum production of ascocarps forS. minimawas obtained with higher concentrations of carbon.Sporormiella isomerarequired an exogenous supply of thiamine for growth and ascocarp production whileS. intermediarequired both thiamine and biotin.Sporormiella minimagrew with thiamine but fruited only with the addition of biotin to the medium. All three species grew well in basic synthetic liquid medium (Containing glucose as a carbon source and potassium nitrate as a nitrogen source) but none of them formed ascoca

ISSN:0008-4026    

DOI:10.1139/b77-219

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A boundary-layer model has been used to describe the movement of dissolved oxygen through a vegetation mat ofWolffiasp. orLemna minor. In an environment where light and temperature are held constant, the reaeration rate of the water below the mat is a linear function of mat thickness. In the light, the rate of oxygen transfer into water through a 10.5-mm mat is 4.4 times higher forWolffiaand 2.9 times higher forL. minorthan in the dark. In the light the rate of oxygen transfer throughWolffiamats is significantly lower in August and September than in early summer. A seasonal shift in transport rates throughL. minormats has not been conclusively established. The efficiency of gas transfer through washedWolffiaandL. minormats 8 to 16 mm in thickness varies from 4.0 to 47.0% of the estimated gas exchange rate for a small protected lake. The rate of gas transfer through the mat is higher than might be expected considering the close packing of the component fronds. The shape of the oxygen profile in the upper portion of a photosynthetically active mat indicates that much of the oxygen produced by photosynthesis of the submerged fronds may be lost to the atmosphere.When the light intensity falls below the level required to exceed the compensation point, dissolved oxygen levels in the water trapped between the fronds are quickly reduced to very low tensions despite the proximity of the entire mat to the oxygen-saturated air–water interface.

ISSN:0008-4026    

DOI:10.1139/b77-220

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Transcellular osmosis measurements are combined with measurements of the kinetics of relative length change, whenChara corallinacells are transferred from artificial pond water to polyethylene glycol (mol wt 300 to 400) of higher osmotic pressure to yield the constantk, which relates relative volume change ΔV/Vto relative length change Δl/l(ΔV/V = kΔl/l). The value ofkis 3.5 and is temperature independent between 7 and 30 °C. Static and kinetic estimates of the bulk modulus, ϵ, indicate that ϵ is temperature independent and has a value between 500 to 650 bars at high turgor pressures. The value of ϵ declines as the turgor pressure declines. We show how ϵ andkare related to Young's modulus and to Poisson's ratio for anisotropicC. corallinacell walls and point out that the previous treatments of the problem are in error.

ISSN:0008-4026    

DOI:10.1139/b77-221

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Twenty-eight species in six genera are recognized, described, illustrated, and their distribution in the province of Ontario and adjacent Quebec and Manitoba recorded. Keys based on fungus morphology provide access to the species treated and an alternate access is given by a generic host index. New hosts and new distribution records are noted within species treatments.MicrosphaeraonVaccinium, long regarded in North America as part of the complex speciesM. penicillata, is given species recognition asM. vaccinii.

ISSN:0008-4026    

DOI:10.1139/b77-222

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Well preserved, permineralized plant material from the Middle Eocene, Allenby Formation of British Columbia provides the basis for this description of an extensive Tertiary flora. The flora comprises a diverse assemblage of abundant plant remains in a chert matrix which outcrops south of Princeton, B.C., Canada. Preliminary examination of this material reveals numerous fertile and vegetative organs of angiosperms, conifers, ferns, bryophytes, and fungi, most of which represent presently unknown taxa. Initial studies indicate that we are dealing with the most diverse Eocene permineralization flora ever discovered. Superb anatomical preservation, including developmental stages of various organs, characterize many of the taxa and promise to significantly increase our knowledge of early Tertiary plants.

ISSN:0008-4026    

DOI:10.1139/b77-223

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Patterns of conidial release byHelminthosporium turcicumPass. (Trichometasphaeria turcicaLuttrell) on sweet corn (Zea maysL.) were studied over 24-h periods under controlled environmental conditions. During the night (dark for 10 h, 100% relative humidity (RH)), relatively few conidia were trapped below diseased seedlings and there were no obvious peaks of spore release. During the day (light for 14 h, 70% RH), however, many conidia were caught (usually four to six times as many as during the night), and there were either one (with 10-week-old seedlings) or two (with 6-week-old seedlings) peaks of spore release. Conidia trapped during the day period were considered to have been released as a result of drying of the leaves. Those trapped during the night were considered to have been washed passively from leaf surfaces. No evidence was obtained to link conidial release with increasing RH.

ISSN:0008-4026    

DOI:10.1139/b77-224

出版商:NRC Research Press    

年代:1977

数据来源: NRC