摘要:

The cambium in black locust consists of several layers of cells at all times. Cambial reactivation (division) is preceded by a decrease in density of cambial cell protoplasts and cell wall thickening but not by cell enlargement. During the resumption of cambial activity, periclinal divisions occur throughout the cambial zone. Early divisions contribute largely to the phloem side. The period of greatest cambial activity coincides with early wood formation. Judged by numerous collections made during two seasons (October, 1960‐October, 1962) the seasonal cycle of phloem development is as follows. Phloem differentiation begins in early April, ends in late September. The amount of phloem produced is quite variable (range: 1‐10 bands of sieve elements per year). Cessation of function begins with the accumulation of definitive callose in the first‐formed sieve elements and spreads to those more recently formed. By late November all but the last‐formed sieve elements are collapsed. All sieve elements are collapsed by mid‐winter and before the resumption of new phloem production in spring. Phloem differentiation precedes xylem differentiation by at least 1 week, and apparently functional sieve elements are present 3 weeks before new functional vessel elements. Xylem and phloem production ends simultaneously in most trees.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1967.tb06903.x

出版商:Wiley    

年代:1967

数据来源: WILEY

摘要:

The form of woody plants is commonly interpreted in terms of apical dominance. Trees with the decurrent or deliquescent branching habit are said to have weak apical dominance, whereas excurrent branching is associated with strong apical dominance. A close examination of many decurrent species such as the oaks, hickories, and maples reveals that almost all of the lateral buds on the current year's twigs are completely inhibited. This complete inhibition of lateral buds by definition and common usage of the term is an expression of strong apical dominance. In trees possessing the excurrent branching habit, such as most conifers and some angiosperms, many of the lateral buds on the current year's twigs elongate to varying degrees. This is usually interpreted as an expression of weak apical dominance. The relationship between bud inhibition and form in woody perennials is much more complex than bud inhibition in herbaceous plants because of the time sequence in the formation and release of lateral buds. For example, it is only after a period of rest or dormancy in the decurrent forms that one or more of the uppermost lateral buds are released, and these may outgrow the currently elongating terminal shoot resulting in forking. Conversely, in the excurrent forms, it seems that the initial expression of weak apical dominance enables the terminal leader to outgrow the currently elongating lateral branches so that it exerts complete control over their subsequent growth and development in later years. An examination of the levels of diffusible auxin at different points along the twigs of excurrent and decurrent species indicates that the balance of growth factors at any given locus, and not the absolute quantity of auxin, exerts primary control over bud inhibition and shoot elongation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1967.tb06904.x

出版商:Wiley    

年代:1967

数据来源: WILEY

摘要:

Auxospore formation has been observed in two marine clones of the diatom genusCoscinodiscus.In each of these clones the variation in valve morphology and structure before and after auxospore formation is appreciable. This variability suggests a reappraisal of the taxonomic characters within the genus will be required if the kinds and types of variation noted are substantiated in other clones. The clones are monecious and the 32 uniflagellate colorless monads, inferred from indirect evidence to be male gametes, form within an undifferentiated mother cell. The method of release of the male gametes differs in the two clones; otherwise their development is similar. The zygote is recognizable and the formation of large diameter cells within the zygote membranes has been observed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1967.tb06905.x

出版商:Wiley    

年代:1967

数据来源: WILEY

摘要:

The major center of variability in the genusTrilliumoccurs in the southern Appalachian mountains of the eastern United States. The karyotypic variation existing withinT. cuneatumRaf.,T. grandiflorum(Michx.) Salisb.,T. erectumL., andT. gleasoniFern., the four most abundantTrilliumspecies in western North Carolina, was analyzed and compared with the variation in gross morphology and the ecological associations of the respective species. The number of types of each kind of chromosome (A‐E), as exhibited following “nucleic acid starvation” by cold treatment, varied widely from species to species. Chromosome types varied within each species and within populations in the numbers, sizes, and positions of euchromatic and heterochromatic segments. No 10‐chromosome karyotype and only one 5‐chromosome complement was found to be duplicated in any two plants which belonged to different species.Trillium cuneatumwith eight chromosome types was morphologically stable and occurred in a limited geographic area.Trillium gleasoni, characteristically adapted to elevations near 2,000 feet, contained 32 chromosome types and exhibited a high morphological variability.Trillium erectum(25 types) andT. grandiflorum(23 types) were also intermediate in morphological variability. These two species had the widest geographical range. Karyotypes were analyzed from pure stands of each of the four species and for each species from mixed stands of two or more of the species growing in close association. TheseTrilliumspecies are maintaining a high level of karyotypic and gross morphological variability within comparatively limited geographical areas. None of the observed karyotypes in any species is likely to have arisen by recent interspecific hybridization. The composite karyotype of each species could be used as an aid to classification in the genusTrillium.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1967.tb06906.x

出版商:Wiley    

年代:1967

数据来源: WILEY

摘要:

A nucleic acid component (x‐RNA) has been found in high concentration in maize shoots. It is eluted from a MAK (methylated albumin kieselguhr) column at about the same position as messenger RNA. The amount of x‐RNA in pea epicotyls is absent or very low. It is suggested that x‐RNA is long‐lived messenger RNA and is found in high concentration in monocotyledonous plants, especially in the case of plants of the Gramineae family. Dicotyledonous plants, typically, contain little or no detectable x‐RNA as observed by ultraviolet absorbancy. In the case of corn shoots, x‐RNA is in highest concentration in the ribosomal fraction (78,500 ×g, 70 min). In both maize shoots and pea epicotyls the newly synthesized nucleic acids were confined to the nuclear fraction (10,000 ×g, 10 min).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1967.tb06907.x

出版商:Wiley    

年代:1967

数据来源: WILEY

摘要:

The ability to observe for extended periods of time individual tobacco cells growing in microculture has made it possible to describe the behavior of their nucleoli and contracting nucleolar vacuoles. Nucleoli typically disappeared in prophase and reappeared in telophase. If several nucleoli were present in telophase they generally fused to form only one or two during interphase. In one instance a nucleolus was seen to separate into two nucleoli prior to disappearance in late prophase. In aging and senescent cells the number of nucleoli or bodies similar to normal nucleoli often increased, and occasionally fragmentation of nucleoli was noted prior to death of cells. Budding of solid material from the nucleolus was also observed. The amount of nucleolar material decreased rapidly prior to death of tobacco cells. Nucleolar vacuoles were found to be a general and consistent component of tobacco cells in microculture. Nucleolar vacuoles typically formed and contracted repeatedly in interphase nuclei and apparently released a fluid material into the nucleus. Associated with the contraction of the nucleolar vacuoles was a corresponding decrease in diameter of the nucleolus. Nucleolar vacuoles were observed to occur in about 70% of the actively growing cells examined, whereas they were present in only 33% of the senescent or weakened cells. These data indicate a relationship between nucleolar vacuoles and the morphogenic status of the cells. Since it has been shown by others that the nucleolus is an active site of RNA metabolism, it is suggested that the contracting nucleolar vacuoles may be involved in the controlled release of a soluble product associated with RNA metabolism.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1967.tb06908.x

出版商:Wiley    

年代:1967

数据来源: WILEY

摘要:

Chloramphenicol and puromycin at appropriate concentrations inhibited the induction of two‐dimensional growth in the gametophytes of the fernAsplenium niduswithout drastically inhibiting germination and continued filamentous growth. Similar responses to actinomycin D were reported earlier. Radioautographic techniques were employed to study the pattern of ribonucleic acid and protein synthesis in gametophytes which were treated with chloramphenicol, puromycin and actinomycin D. Uptake of H3‐uridine into ribonucleic acid was strongly inhibited by all three antibiotics. Chloramphenicol and puromycin were not as effective as actinomycin D in inhibiting H3‐leucine incorporation. The results are discussed in relation to the quality of light and antibiotics on two‐dimensional growth in the gametophytes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1967.tb06909.x

出版商:Wiley    

年代:1967

数据来源: WILEY

摘要:

Chromosome counts are reported for 76 taxa and 2 natural hybrids of tribe Senecioneae (Compositae). First counts are reported for several species of Senecioneae as well as for the generaCadiscusandWhitneya.New chromosome numbers are added to those previously known inArnica, Cacalia, andSenecio.Additional counts fromArnicasupport our previous suggestion thatx= 19 for this genus. It is assumed that observed meiotic irregularities are associated with apomixis in this genus. Basic chromosome numbers for various New World sections ofSenecioare proposed, and certain problems of sectional relationships in this genus are discussed. Chromosome numbers and plant morphology ofCadiscus, Hulsea, andWhitneyaindicate that these genera should be removed from Helenieae to Senecioneae. The possible affinity of the anomalous genusAdenocaulonwith Mutisieae is discussed. Data presented in the paper further support our earlier proposal that the basic chromosome number for Senecioneae isx= 10.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1967.tb06910.x

出版商:Wiley    

年代:1967

数据来源: WILEY

摘要:

Floral histology and vascular anatomy ofMyristica fragransVan Houtt. andM. malabaricaLam. have been investigated from serial sections and specimens cleared in chloro‐lacto‐phenol. The flowers are unisexual. The androecium is considered to consist of a whorl of laterally concrescent anthers. The bisporangiate anthers are attached by a ridge of tissue to the terminal part of the androphore. In many cases the number of vascular bundles in the androphore is half the number of anthers. The gynoecium consists of a monocarpellate pistil with basal placentation and a single anatropous ovule. Of the many vascular bundles that enter the base of the carpel, two, because of their position and because they provide vascular traces to the ovule, are designated as ventral bundles. Additional ovular traces are provided by the carpel wall vascular system. These additional traces originate at the top of the locule and descend to the ovule. The similarity between the androecia of these two species and the androecium of the ćnellaceae is noted.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1967.tb06911.x

出版商:Wiley    

年代:1967

数据来源: WILEY

摘要:

The genomic relationships between modernFragariadiploids (European and AmericanF. vescaandF. viridis—2n= 14) and octoploids (F. virginianaandF. chiloensis—2n= 56) were investigated. This contrasts with previous studies where cultivars have represented the octoploids. Critical information on genomic pairing was obtained by comparing chromosome behavior of pentaploid hybrids with that of hexaploid hybrids (obtained by using a recent colchiploid of EuropeanF. vesca). Supporting data were also used from anF. chiloensis × Potentilla glandulosahybrid (2n= 35). A revision of theAABBBBCC(Federova) genomic formula for the octoploids toAAA'A'BBBBis proposed based upon cytological evidence of homology between theAAand“CC”genomes. The phylogeny of the octoploids is postulated.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1967.tb06912.x

出版商:Wiley    

年代:1967

数据来源: WILEY