摘要:

This, paper reviews five premises which underlie the simple Münch-type pressure-flow mechanism of sugar transport in plants from source to sink. The validity of each of these has been found experimentally to be in doubt in functioning sieve tubes, but at least four of the five should pertain if the simple pressure-flow theory is valid. A brief survey of alternate suggestions of mechanisms for sugar transport is given in the light of recent findings; in particular, models which reconcile ATP-assisted flow with pressure flow are discussed.

ISSN:0008-4026    

DOI:10.1139/b81-060

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The complete life history ofHalosaccion ramentaceumhas been determined. It is very similar to that ofPalmaria palmata, consisting of haploid male and female gametophytes alternating with a diploid tetrasporophyte. As forP.palmata, there is no carposporophyte. Male and female gametophytes attain sexual maturity almost a generation apart. Whereas male plants require approximately 1 year's growth before producing spermatia, female gametophytes are microscopic and reach sexual maturity only a few days after tetraspore germination. The diploid tetrasporophyte initiates its development on the female, but almost immediately forms an independent holdfast on the substratum beside the female. The first diploid fronds arise from that holdfast after it is well established.The existence of a complete sexual cycle was proven by demonstrating: fertilization of trichogynes by spermatia; meiosis in tetrasporangia, with a chromosome number ofn = ~24 in gametophytes and 2n = ~48 in tetrasporophytes; and by documenting the Mendelian transmission of a mutant phenotype from the male parent to the F1gametophytes.

ISSN:0008-4026    

DOI:10.1139/b81-061

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

InRamalina,Trichoramalina, andFistularieliathe cortex is two layered, composed of an external layer of variable thickness and an inner layer of periclinally arranged mechanical tissue. The outer layer is a reticulate network of branching cells in a gelatinous matrix which is very thin or absent in patches in some species. The inner layer may be a uniform chondroid sheath or a series of internal ribs, often extending into the medullary region, and is composed of more or less periclinal, longitudinally aligned hyphae.DieverniaandRamalinopsishave a single tissued cortex which is derived from the external cortex of aRamalinacortex with the mechanical tissue lacking. The lower cortex inRamalinopsisis melanized and has occasional fascicles of mechanical tissue.Nieblaspecies exhibit three intergrading cortical arrangements. TheN.homaleagroup and other species with a bladelike morphology have a thick outer cortex with palisade cell lines and a subtending layer of supportive tissue. Most species have conspicuous chondroid strands in the medulla which are not attached to the cortex and may form from medullary hyphae. TheN.ceruchisgroup, composed of terete plants, have a thin cortex of branching hyphae in a matrix with mechanical tissue either absent or sparsely present. Chondroid strands are usually poorly developed, and are only a few cells thick in the medulla. The saxicolousN.combeoidesgroup, derived from theN.ceruchisline, have a thick mechanical layer and a variable palisade layer. Chondroid strands are very sparse or absent.Cenozosia, a monotypic genus endemic to South America, is anatomically similar to South AmericanN.ceruchis. This hollow species has frequent chondroid strands which crisscross the lumen of the branches in some morphs.

ISSN:0008-4026    

DOI:10.1139/b81-062

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Light microscopic studies ofBipolaris maydisrace T demonstrated that a fibrillar sheath, often several times the hyphal diameter, can be observed when the hyphae are negatively stained with India ink or treated with fluorescent antibodies or diaminobenzidine. Sheaths were observed on hyphae incubated under a variety of cultural conditions and on race O ofB.maydisas well as on other species ofBipolaris. Sheaths were found only on rapidly growing hyphae such as tips and germ tubes; conidia and hyphal segments older than approximately 72 h lacked a sheath. Examination of the hyphae using electron microscopy confirmed the age-dependent nature of the sheath and suggested that the lack of this structure on old hyphae is due to the deposition of a pellicle on the hyphal surface.

ISSN:0008-4026    

DOI:10.1139/b81-063

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Caryopses ("seeds") ofCalamovilfa longifolia(Hook.) Scribn. are dimorphic (brown and white) and are each enclosed in a lemma and palea. The most complete germination was obtained in lighted (fluorescent light of 1600 lx) growth chambers set at alternating temperatures of 25 °C day (14 h) and 10 °C night. Seed stratification did not increase total germination but the rate of germination was increased. The seeds imbibed about 50% by weight of water before germination was initiated.Under field conditions seeds accumulated in depressions. Seedlings failed to emerge from depths greater than 6 cm. The survival rate of seedlings was very low (0.5%) during 1978 because of a dry summer but was considerably higher in 1979 on south slopes (33%), under willow clumps (44%), and on north slopes (56%). Seedling mortality was due to high soil temperatures, desiccation, burial or exposure of seedlings, and biotic agents. Seedlings emerged from the soil mainly by elongation of the first internode. The coleoptile seemed to act as a protective sheath against high soil temperatures for the growing point enclosed within it. A significantly linear increase in height of seedlings, root length, and number of leaves occurred with an increase in the age of seedlings during both years.

ISSN:0008-4026    

DOI:10.1139/b81-064

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Effects of postfumigation temperature on SO2-fumigated seedlings of red pine (Pinus resinosaAit.) were studied. Seedlings were fumigated with either 0.2 ppm SO2for 91 h or with 0.5 ppm SO2for 30 h. Seedling injury was much greater at the higher SO2concentration. At the lower SO2concentration, only root weight of fumigated seedlings was affected, and it was about 20% less than that of unfumigated controls after 6 weeks at 12, 22, or 32 °C; there was no interaction between SO2treatment and postfumigation temperature on growth rate. Postfumigation growth was reduced more by the higher concentration of SO2. Significant interaction between SO2and postfumigation temperature occurred, with growth of roots, primary needles, and secondary needles being reduced most at 12 °C. At higher postfumigation temperatures, SO2-fumigated seedlings recovered (partially) and initiated secondary needles, thereby providing a new source of photosynthate and further reducing growth inhibition. But at 12 °C, shoot growth was slow and injured needle tissue was not replaced; hence the dry weight of roots of plants fumigated at the higher SO2concentration was <30% of that of controls after 6 weeks. Interpretation of effects of fumigation temperature on SO2toxicity should also consider influences of postfumigation temperature regimes.

ISSN:0008-4026    

DOI:10.1139/b81-065

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Height growth in hemlock (Tsuga canadensis(L.) Carr.,T.heterophylla(Raf.) Sarg.,T.mertensiana(Bong.) Carr.) is by rhythmic growth of a monopodial axis with continuous branch production throughout the growing season. Leader growth is plagiotropic and leader erection is a process lasting several years. Two types of events disrupt the basically monopodial nature of the axis. (1) Frequent (43%) apical meristem death shifts dominance to a nearby lateral branch inT.canadensis. (2) Weak apical control allows occasional shifts in dominance from the leader to a branch without meristem death (13 and 24% inT.heterophyllaandT.canadensis, respectively, but none inT.mertensiana). These growth patterns contain elements of several tree architectural models but fit none well.

ISSN:0008-4026    

DOI:10.1139/b81-066

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Black locust (Robinia pseudoacaciaL.), a native species of North America, has found a specific and efficientRhizobiumstrain in French soils. Ultrastructural studies of young nodules showed that infection of the host cell occurred by numerous infection threads. Rhizobia are liberated in the cell by endocytotic processes. No important differences were found between rhizobia in the infection threads and bacteroids in the host cell; the bacteroid cells were only enlarged, without any structural change. ThisRhizobiumstrain is a "fast grower".Roots were also infected by an endomycorrhizal fungus producing numerous vesicles and arbuscules in the root cortex.Nitrogen-fixing activity, assayed by the acetylene reduction method, was measurable only 5 to 10 days after nodular development. Until the 50th day after seed germination, the activity increased slowly, then more rapidly. By the 80th day, fixing activity was about 9 μmol/h per plant.No relationships between the form, age, and fixing activity of the nodules were found.

ISSN:0008-4026    

DOI:10.1139/b81-067

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The toxicity of a range of potassium salts of fatty acids was bioassayed againstBotrytis cinereaPers. in agar culture. Growth inhibition increased with number of carbon atoms of the short chain fatty acid salts, reached a peak around C10(caprate), and then declined. Salts of dicarboxylic acids were nontoxic at the highest levels tested, while the unsaturated C11:1, undecylenate, was as potent as caprate. Caprate at 0.1% inhibited growth of mostB.cinereaisolates tested and prevented the remaining isolates from forming sclerotia. Conidial germination of all isolates was prevented by 0.05% caprate. Discrepancies in the literature regarding control ofB.cinereawith soft soaps are suggested to be due to varying fatty acid composition of the soaps used.

ISSN:0008-4026    

DOI:10.1139/b81-068

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Floral development in the speciesPotamogeton zosteriformisis compared with that of other species ofPotamogetonpreviously investigated (P.densusandP.richardsonii). A spike inflorescence is found on which 6 to 20 flowers develop. These flowers develop their appendages acropetally; first, the four tepals are initiated followed by the four stamens opposite the tepals. As in the flower ofP.densus, the two lateral stamens are each initiated as two separate primordia. Unlike any otherPotamogetonspecies where four carpels generally arise, alternating with the tepal and stamen pairs, inP.zosteriformisa single carpel consistently develops on the central portion of the remaining floral meristem. Histological preparations did not reveal any vestigial procambial strands differentiating in the gynoecium. This unique floral development is examined from several points of view. Morphogenetic comparisons are made with other species ofPotamogetonwhich develop tetramerous gynoecia. Morphologically the nature of thePotamogetonflower is reexamined and phylogenetically the possibility ofP.zosteriformisas a link or transition between the bisexual and unisexual groups within the Najadales is considered.

ISSN:0008-4026    

DOI:10.1139/b81-069

出版商:NRC Research Press    

年代:1981

数据来源: NRC