摘要:

Some plants require only one 24‐hr cycle of the appropriate photoperiod to be induced to flower; others require seven or more. To try to understand the basis for this striking difference, the length of the leaf plastochron was determined forXanthiumandPerillain the same experiments in which their sensitivity to various numbers of photoperiodic cycles was measured. The general finding was that for full floral induction there had to be as many 24‐hr inductive cycles as there were days in the plastochron. When the total days in the plastochron were altered by environmental manipulation, the cycles required for floral induction altered in parallel.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10114.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

During the annual three‐phase growth cycle of white spruce [Picea glauca(Moench) Voss] the vegetative shoot apex changed in anatomical configuration. Relative amounts of DNA, histones, RNA, and proteins were measured in three cytohistological zones and were related to the anatomical changes during ontogeny. An extended period of DNA synthesis (S) and G2preceded an increase in the number of apical initial cells which were part of the mammillary apex. While DNA and histones were generally synchronous during ontogeny, the ratio of DNA to histone increased on June 20. This loss of histone and subsequent increases in RNA and cytoplasmic proteins preceded the appearance of needle primordia on next year's apex. We propose that induction of the apex to reorganize and form needle primordia occurred when the DNA was in a 2C condition, following the loss of histone on June 20.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10115.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Ethylene, a natural product of sensitive fern(Onoclea sensibilisL.) gametophytes, has been demonstrated to inhibit cell division in light‐grown prothallia. When plants were grown on Knop's solution plus 1 % sucrose under 300 ft‐c or more of white light, all ethylene concentrations from 1–1000 μl/liter reduced the rate of increase of cell number by about one‐half. The over‐all rate of increase of cell number was regulated by various environmental and chemical factors, but regardless of the rate established in control cultures, ethylene treatment of 1–1000 μl/liter produced a relative 50 % depression of cell number. Ethylene was specific for inhibition of cell division and was not a general inhibitor of growth. The ethylene inhibition did not result from a reduction of photosynthesis or energy supply. Further demonstration of ethylene as the active gaseous component resulted when cultures were grown in small enclosed containers with an ethylene absorbent, mercuric perchlorate, and consequently the cell number of gametophytes was restored to the level of unenclosed controls.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10116.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Spores ofOnoclea sensibiliswere investigated for inhibition of germination by ethylene. A curve of germination against ethylene concentration indicated a “threshold” type of response, but percentage of spore germination was not influenced either by the density of the inoculum or by the presence of 1 % sucrose in the culture medium. Ethylene totally inhibited dark germination, but in white light reversal of inhibition was possible in about 50% of the germinating spores. Time‐course studies revealed that in imbibed spores ethylene inhibited germination in the first 3 ± 1 hr of illumination. Dose‐response curves of light intensity vs. germination indicated that the response to light differed in the presence and absence of ethylene. Recovery from inhibition was possible once ethylene was allowed to escape, and the rate of recovery was accelerated by light.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10117.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

A range of phyllotactic variation inZea mayshas been obtained from progeny derived from a single ‘opposite‐leaved’ plant. Some segregants exhibit a form of alternate phyllotaxy with poor separation between nodes, while others duplicate the original decussate condition. Numerous intermediate examples have also been observed. Some have both spiral and opposite arrangements on the same plant; others, which begin their ontogeny with the normal distichous arrangement, switch at different stages of maturity to spiral or decussate arrangement. Leaves from ABPHYL plants are up to one‐half the width of comparable normal leaves although their length is similar. Since ABPHYL plants may have twice as many leaves as do normal siblings, total area and dry weight of leaf blades per ABPHYL plant are greater than in normal siblings. Leaf width of both ABPHYL and normal plants correlates well with the number rather than the width of epidermal cells.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10118.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Analyses of ploidy levels in progenies from 2x x 2x, 2x x 4x, 4x x 2x, 4x X 4x, and 4x x OP crosses during embryogenesis and seed germination indicate that the progenies include an array of aneuploids. The occurrence of some of the aneuploids was previously unreported. Most of the aneuploids were from 2x x 4x crosses, which yielded the largest number of progeny. Chromosome counts from embryos and endosperms of sectioned young seeds provide evidence that aneuploids originate in progenies of 2x x 4x crosses from the functioning of male gametes with more or fewer chromosomes than 2x = 18 in syngamy with reduced and unreduced female gametes. The origins of aneuploids in progenies from other crosses are problematical at this writing.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10119.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Clonal cultures ofCodium fragilewere established from both swimming cells and vegetative filaments. In the laboratory axis primordia differentiate from heterotrichous juveniles only when cultures are agitated on a reciprocating shaker. The shear forces created by mechanical agitation are essential both for initiation and maintenance of primordia. Contact guidance of growing coenocytic filaments indicates mutual adhesion of filaments as the basis for the differentiation process.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10120.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Chromosome numbers of 2n = 20, 24, 36, and 38 were found in the various taxa comprising theEleocharis tenuiscomplex in the United States.Eleocharis tenuisvar.verrucosa, the only taxon in the complex with 2n = 20 is given the new status of a full species[E. verrucosa(Svens.) Harms] and seems most closely allied to two southern members of the subseriesTruncataewhich are not members of thetenuiscomplexs. s. Karyotypes and meiotic pairing in artificial hybrids indicate that the remainder of the taxa are derivatives of X = 6 withE. tenuisand one of two cytotypes ofE. compressawith the lowest numbers of 2n = 24, although evidence is presented to indicate that they are of amphidiploid origin. A second cytotype ofE. compressawith 2n = 36 is a segmental autoallohexaploid, whereasE. ellipticaandE. ellipticavar.pseudoptera(Svens.) Harms,comb. nov. with 2n = 38 are hyperploid derivatives of 2n = 36.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10121.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Four populations ofMimulus glabratusvar.utahensisPennell from the Great Basin and seven ofM. glabratusvar.fremontii(Bentham) Grant from the New Mexico–Texas–northeastern Mexico area were intercrossed and their F1hybrids grown. Cytology and fertility of both the parental populations and the F1hybrids were studied. The following cytological abnormalities were observed in microsporogenesis: cytomixis, the stretching of one or more chromosomes from cell to cell; multipolar divisions, separation of the chromosome complement into two or more parts; unequal disjunction; spontaneous polyploidization; and the production of encapsulated pollen tetrads. Typically, these abnormalities were rare or not observed in the parents, were rare in the intravarietal hybrids, but were more common in the intervarietal hybrids. They were closely associated with, in fact were the probably causes of, barriers to gene exchange between these two diploid (n = 15) varieties. Thus, the apparent causes of barriers to gene exchange in intervarietal hybrids are the likely mechanisms for the evolution of aneuploidy and polyploidy so characteristic of the rest of theMimulus glabratuscomplex.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10122.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

The anatomy of three species ofGymnophytonhas been studied by light and electron microscopy. The species are essentially leafless and morphologically they are very much alike, but they differ anatomically and can be characterized just by their anatomical differences. SEM revealed great differences in stomatal structure, orientation, and dimensions. Micro‐channels (ectodesmata) in the guard cell walls were disclosed in great numbers inG. isatidicarpumby using interference contrast microscopy, and these structures are thought to function as pathways for wax precursors. In older stems of this species the epidermis and cortical palisade tissue are isolated by a continuous periderm layer. Before dying, the palisade cells undergo alterations, and the stomata are permanently closed by cuticular plugs between the guard cells or by fusion of the swollen adaxial parts of the subsidiary cells. Similar permanent closure mechanisms are not found inG. polycephalumandG. robustum, which also deviate by having their stomatal openings orientated at a right angle to the axis of the stem and by the occurrence of collenchyma strands instead of fiber strands along the stem corner ribs.Gymnophyton polycephalumandG. robustumseem to be more closely related to each other than either is toG. isatidicarpum, but they differ markedly from one another in the size and structure of their stomatal complexes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10123.x

出版商:Wiley    

年代:1972

数据来源: WILEY