摘要:

In coniferous stems the rate of multiplication of fusiform initials in the vascular cambium by means of pseudotransverse division often fluctuates considerably around the circumference. In fluted stems the frequency of these divisions is appreciably higher and the ratio of survival of the newly formed initials relative to the rate of production lower in the depressions than in the adjoining convex portions of the perimeter. The probability that compression is a factor tending to accelerate the frequency of anticlinal division is indicated by the decided increase in rate in areas of the stem subjected to radial pressure. Higher frequencies of pseudotransverse division are accompanied by reduction in mean cell length of the cambial cells and hence of the derived wood elements.

ISSN:0008-4026    

DOI:10.1139/b57-036

出版商:NRC Research Press    

年代:1957

数据来源: NRC

摘要:

Walls of elongating parenchyma and epidermal cells ofAvenacoleoptiles and onion roots were studied by autoradiography, using C14-labelled sugars, and by electron microscopy of thin transverse sections. The autoradiographs showed that deposition of cellulose takes place over the whole length of the cell, ruling out the possibility of bipolar tip growth. Autoradiographs of cells grown for short times in labelled sugar gave no evidence of localized incorporation of isotope around primary pit-fields, but rather indicated that deposition of microfibrils is finely dispersed over the entire wall surface. The thin sections revealed a marked change in wall structure as elongation proceeds. Walls of young cells contain only transversely oriented microfibrils while older walls include an inner region of predominately transversely oriented microfibrils bounded outside by a region with microfibrils showing an irregular transition to longitudinal orientation. The degree of longitudinal orientation in the outer region increases with cell length. These results for thin walls are consistent with the multi-net model for wall growth deduced by other workers from electron microscope studies on cell fragments. Thin sections have also revealed layering in several types of growing walls which is difficult to interpret on the basis of the multi-net model alone.

ISSN:0008-4026    

DOI:10.1139/b57-037

出版商:NRC Research Press    

年代:1957

数据来源: NRC

摘要:

The growth of wheat seedlings under aseptic conditions is shown to be well supported byL-alanine, glycine, and urea, but not so well as by nitrate. On the other hand,D-alanine and the optical isomers of leucine exerted toxic effects; seedling growth in these solutions was less than in the cultures receiving no nitrogen, and the presence of nitrate in the nutrients did not reduce their toxic effects. However, the toxic effect ofD-alanine was partially offset byL-alanine. A somewhat parallel influence upon the growth of wheat seedlings andP.parasiticawas exerted byD- andL-alanine,D- andL-leucine, and glycine, but not by urea. The latter poorly supported the fungus although it helped the growth of wheat.D-leucine is more toxic toP.parasiticathanL-leucine, less toxic to wheat seedlings as measured by growth inhibition, but more toxic as measured by chlorotic lesions in the foliage.

ISSN:0008-4026    

DOI:10.1139/b57-038

出版商:NRC Research Press    

年代:1957

数据来源: NRC

摘要:

Little Club (rust reaction type 4) and Khapli (rust reaction type 1 with race 15B) wheats were grown in sand culture in 1-qt. crocks or 5-in. pots. Daily applications of maleic hydrazide or indoleacetic acid were started 5 days before (10 days after sowing), on the day of, and 5 days after inoculation with stem rust (Race 15B) and were continued for about three weeks. Maleic hydrazide inhibited growth and, at 5 and 10 mg. per pot, flowering. Type 4 pustules developed on Khapli plants treated with 5 and 10 mg. of maleic hydrazide daily from the 5th day before and from the day of inoculation. Indoleacetic acid (0.5 mg. per pot from the 10th day after sowing) stimulated growth and flowering and slightly increased the resistance of Khapli. Treatments started 5 days after inoculation had no effect on rust development on Khapli, and none of the treatments altered the rust reaction of Little Club. Spores produced on plants treated with maleic hydrazide gave normal rust reactions on untreated plants.The effect of maleic hydrazide on the plants and on rust development was not altered by the simultaneous application of uracil, which reversed the growth inhibition caused by thiouracil. Thiouracil inhibited rust development in the presence of maleic hydrazide.

ISSN:0008-4026    

DOI:10.1139/b57-039

出版商:NRC Research Press    

年代:1957

数据来源: NRC

摘要:

Khapli wheat was grown in sand culture in 1-qt. crocks. Daily applications of maleic hydrazide (10 mg. per crock) were started about 10 days after sowing. After 5 to 12 or 15 days of treatment, samples were taken for analysis. Maleic hydrazide inhibited growth and caused increases in the dry weight, total soluble matter, sucrose, and free amino compounds, particularly glutamine and glutamate, in the first leaves. The treated leaves were also rich in starch which does not normally occur in the wheat leaf.

ISSN:0008-4026    

DOI:10.1139/b57-040

出版商:NRC Research Press    

年代:1957

数据来源: NRC

摘要:

An ontogenetic study of adventitious stem formation on root segments of creeping-rooted alfalfa clones is presented. Unusual meristematic activity is evident first in the phellogen near a lateral rootlet. Continued activity in that region gives rise to a primordial dome from which adventitious stems eventually emerge. Concomitantly, in the subjacent phloem parenchyma cells dedifferentiation and subsequent redifferentiation into vascular tissues occurs. Thus a vascular system is formed which extends from the adventitious stems to the cambium region of the root and, in some instances, to the cambium of the lateral rootlet. Adventitious stems are initiated in secondary tissues of the root. Factors such as age of root, culture treatment, and inherent differences have an influence on adventitious stem initiation.

ISSN:0008-4026    

DOI:10.1139/b57-041

出版商:NRC Research Press    

年代:1957

数据来源: NRC

摘要:

Development ofZostera marinaL. is described from proembryo to mature seed. The single cotyledon and the stem apex develop laterally from the nearly spherical young embryo. No radicle is produced; the hypocotyl develops into a swollen basal part (the original embryonic mass) and an elongated axial part formed by cell divisions at the base of the cotyledon and plumule. The cotyledon grows in part by cell divisions at its apex. Curvature develops in the axial hypocotyl mainly by unequal elongation of cells, whereas curvature of the cotyledon is mainly by unequal increase in cell numbers. A single procambial strand differentiates from the suspensor end of the basal part of the hypocotyl through the axial part into the cotyledon and plumule. The plumular stem apex develops a single-layered tunica over a several-layered corpus. It produces three leaf primordia, one with air-spaces organized, before dormancy sets in. Mid-vein procambium differentiates acropetally from the axial strand into each leaf primordium; lateral procambial strands differentiate acropetally and basipetally from near the base in each of the first two primordia. Two adventitious root apices differentiate external to the axial procambium at the base of the cotyledon. Seed coat development is described briefly. The nucellus remains a non-vascularized column of cells extending upward from the highly vascularized attachment region of the seed. The patterns of development reported support the interpretation that the starchy, shield-shaped main part of the embryo is the basal part of the hypocotyl and that the first leaflike structure is the cotyledon.

ISSN:0008-4026    

DOI:10.1139/b57-042

出版商:NRC Research Press    

年代:1957

数据来源: NRC

摘要:

Histological studies of the host–parasite relationships betweenSeptoria glycinesHemmi and soybean have revealed that penetration is stomatal without, the presence of an appressorium. Subsequent spread of the pathogen is intercellular in the mesophyll tissue and in the parenchyma sheath and phloem of the leaf veins. While the fungus does not show marked action in advance and requires to be in intimate contact with vital cells in order to progress through host tissue, its fruiting bodies are matured only in the holonecrotic region of the lesion. The fungus seems incapable of invading the plesionecrotic zone which borders the holonecrotic region; the role of this zone in limiting the pathogen to a discrete spot has been discussed.Colonization of the pericarp and seed is primarily intercellular, although intracellular hyphae may be found in the sclerenchyma of the subhilum region of the seed. Infection of the seed may occur directly at the point of contact of the seed with the wall, or by systemic invasion via the placenta and funiculus. This study establishes conclusively thatS.glycinesis seed-borne in the soybean.

ISSN:0008-4026    

DOI:10.1139/b57-043

出版商:NRC Research Press    

年代:1957

数据来源: NRC

摘要:

The speciesKoenigia islandicaL. may be assumed to be the most hardy of all annuals, since it occurs at higher altitudes and latitudes than any other therophyte. Its area of distribution, restricted to the Arctic, though with offshoots to some temperate mountains, is practically circumpolar. In Asia, it has long been known from the Tien Shan at about 40° lat. N. In Europe, its southern limits are on the Isle of Skye at about 50° 30′ lat. N., while in North America its southernmost locality was a little north of Jasper in the Canadian Rockies until its discovery a few years ago in Colorado just south of the 40th parallel. A closely related species is known to occur in the southern parts of Tierra del Fuego. Specimens from the Faeroes, Greenland, Iceland, Scandinavia, and Colorado are morphologically and cytologically inseparable, being characterized by the tetraploid chromosome number 2n = 28. Though the genus is usually regarded as mono- or bi-typic, (1) it is pointed out that some species, often included inPolygonums.lat., really belong toKoenigiain a somewhat wider sense; in addition to morphological similarities, they are characterized by the basic chromosome numberx = 7, which is rare in the family and absent in the Polygoneae s.str. (2) It is also emphasized that the division of the Polygonaceae into subfamilies has not been successful since evolutionary highly distinct types are traditionally united in the subfamily Polygonoideae. (3) It is proposed that this subfamily be divided into two large subfamilies at the same time asKoenigiaand its closest relatives be treated as a separate taxon at a very high level.

ISSN:0008-4026    

DOI:10.1139/b57-044

出版商:NRC Research Press    

年代:1957

数据来源: NRC

摘要:

Active particles, presumed to be mitochondria, have been isolated by differential centrifugation from the hypocotyls of etiolated soybean seedlings. These particles were capable of oxidizing all Krebs cycle intermediates tested, although fumarate and oxaloacetate were oxidized relatively slowly. Oxygen uptake in the presence of succinate, pyruvate, or ketoglutarate was increased two to four times by the addition of ATP, MgSO4, and cytochromec. Maximum activity was obtained when both sucrose and phosphate were added to the grinding and suspending media, and when the reaction mixture was buffered near pH 7.0. Endogenous oxidation was reduced 50% by one washing and at the same time the oxidation of exogenous substrate was increased two to three times. Average P:O ratios of 0.4, 0.8, and 0.9 were obtained without added hexokinase or fluoride for succinate, pyruvate, and ketoglutarate, respectively. These ratios were increased to 0.8, 1.2, and 1.5 by the addition of hexokinase. In all cases, 10−2 MNaF decreased oxygen uptake 30 to 40% without affecting P: O ratios. Isolated soybean particles appear to be similar in most respects to particles from other plants. Certain differences were found and are discussed.

ISSN:0008-4026    

DOI:10.1139/b57-045

出版商:NRC Research Press    

年代:1957

数据来源: NRC