摘要:

In seedlings ofIpomoea purpureasecondary roots are initiated in the primary root pericycle opposite immature protoxylem. Cells derived from immature endodermis, pericycle, and incipient protoxylem and stelar parenchyma contribute to the primordium. The derivatives of the endodermis become a uniseriate covering over the tip and flanks of the primordium and emerged secondary root; the endodermal covering is sloughed off when the lateral root reaches 1–5 mm in length. A series of periclinal and anticlinal divisions in the pericycle and its derivatives gives rise to the main body of the secondary root. The initials for the vascular cylinder, cortex, and rootcap‐epidermis complex are established very early during primordium enlargement. After emergence from the primary root, the cortical initials undergo significant structural modifications related to enlargement of the ground meristem and cortex, and the rootcapepidermal initials are partitioned into columellar initials and lateral rootcapepidermal initials. Procambium diameter increases by periclinal divisions in peripheral sectors. The mature vascular cylinder is comprised of several vascular patterns, ranging from diarch to pentarch, that are probably related ontogenetically. Cells derived from incipient protoxylem and stelar parenchyma cells of the primary root form the vascuar connection between primary and secondary roots.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05965.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

A collection of over 200 petrified Middle Devonian plants was made from a single locality near Cairo, New York. This paper represents the second of a series enumerating the plants of the flora.Reimannia aldenensewith a single lateral appendage containing a terete xylem strand that divides is present.Reimanniais thought to represent young branches within the Aneurophytales. Many of the sections made for the study of the flora contain small, terete axes. Some have a very distinctive epidermis. Some dichotomize several times.Cairoa lamanekiigen. et sp. n. shows closest affinity to the Aneurophytales yet differs in that the shape of the primary xylem is not consistently repeated from one order of axis to the next. It is suggested thatCairoaandProteokalonrepresent a distinctive subgroup in the Aneurophytales.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05966.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

The protoplast of maturing axial tracheids in the secondary xylem of shortleaf pine (Pinus echinataMill.) was studied by transmission and scanning electron microscopy. The mature protoplast is differentiated into two interconnected components: (1) the commonly observed peripheral layer lining the secondary cell wall, and (2) an elaborate reticulum of cytoplasmic filaments and placoids within the central vacuole. The reticulum provides an extensive surface area of vacuolar membranes for rapid exchange of nutrients and metabolites with the vacuolar sap, which is envisaged to function as a vital medium during the period of secondary cell wall synthesis. The breakdown of the protoplast which terminates tracheid maturation is associated with poorly defined alterations of the vacuolar membranes. This is indicated by increased formation of cytoplasmic spherules and membraneous vesicles which may be portions of separated vacuolar membrane during early stages of degradation. Autolysis is supposed to occur when the cytoplasm is exposed to the vacuolar sap after rupture and separation of the vacuolar membranes. The Gomori acid phosphatase technique as combined with electron microscopy produced no evidence of autolysosomal segresomes in strands of intravacuolar reticulum of the cytoplasm.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05967.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

The organization of the morphophysiological unit inAnagallis arvensisL. is conditioned by vegetative growth, which is expressed as indeterminate under short‐day conditions and as determinate under long‐day ones. The perpetuation mechanism is a function of the environment. Under SD conditions ontogenetic morphogenesis is incomplete, and the unit does not form specific reproductive structures; indeterminate growth and permanent rooting capacity provide an efficient mechanism for perpetuation. Under LD complete ontogenetic morphogenesis assures perpetuation by seeds. The appearance of senescence is independent of the nature of the morphophysiological unit and is directly related to growth cessation. It affects organs only when growth is indeterminate (SD) and the whole organism when growth is determinate (LD). Organ senescence seems related to growth itself, and organism senescence would appear closely related to photoperiodic effects. Photoperiod controls organization of the unit, ontogenetic morphogenesis, and organism senescence simultaneously. The number of leaves per node, flowering, organization, and senescence of the organism are all directed toward a more or less evolved state by the effects of the photoperiodic condition.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05968.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

Eleven of the 12 species ofPachyphytum, all that are available, haven= 31–33 standard chromosomes, or a multiple. Accessory chromosomes were found in some or all collections of four species; some cells of one plant have more than 50 of them. Accessory chromosomes often occur in groups at metaphase I, corresponding to their origin from one to several chromocenters of prophase I. Intraspecific polyploidy occurs within five species, with diploids to 12‐ploids (n= ca. 186) inP. compactumand diploids to decaploids (n= ca. 160) inP. hookeri. Although the basic chromosome number is high, evidence from meiosis in certain hybrids shows that the basic 31–33 chromosomes are probably all different: they do not pair with each other and they do not duplicate each other. Polyploids, with 62 or more chromosomes, are probably autopolyploids: they form multivalents, and the chromosomes they contribute to hybrids pair with each other. Three different probable hybrids have been found in the wild, and more than 300 hybrids have been produced in cultivation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05969.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

Both histological and autoradiographic procedures were used to follow lateral root initiation and development. Lateral roots ofM. sylvestriswere initiated in the pericycle, and although the endodermis became multiseriate, endodermal derivatives were not incorporated into the lateral root primordium. Apical organization of pre‐emergent roots, characterized by two tiers of cortical initials, did not change with growth. During pre‐emergent development there was no evidence of cortical lysogeny or quiescent center formation. Quiescent centers were present in both secondary and tertiary roots longer than 0.5 cm.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05970.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

The structural, flowering, and fruit‐setting patterns of inflorescences of mature Hamlin and Valencia orange and Marsh grapefruit trees were studied for three years. Several development patterns were found, some of which were relatively consistent for the different varieties or years of study. The sequence of anthesis on an inflorescence was: apical flower first, then basal flower, then the subapical flower. Terminals on which the earlier flowers appeared tended to have more inflorescences than those on which flowers appeared later. Inflorescences on which earlier flowers appeared also produced more flowers than those which began flowering later. Inflorescences that began flowering later were more likely to have leaves or have a greater number of leaves than earlier inflorescences. More than half of the inflorescences carried no leaves, and most of these had one flower. No evidence of a relationship between number of flowers and length of the inflorescence was found. Fruit set occurred primarily during the latter part of the flowering period. Many fruit were set on inflorescences without leaves, but on the basis of percent of flowers setting fruit, inflorescences with leaves were more productive. The greatest fruit set occurred in the subapical position on the inflorescence. With growth changes these fruit often appeared to be developing in the apical position. These patterns generally differed little from year to year. Variations may have been due to the differences in the number of flowers produced by the trees. Results were also similar between Hamlin and Valencia oranges. Patterns on Marsh grapefruit resembled those for the oranges but were frequently less consistent.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05971.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

The dwarf‐shoot apex ofPinus monophyllahas a cytohistological zonation typical of pines. Cataphylls are initiated by this apex both before and after the dormant winter period. The needle is initiated in the spring of the same season in which it matures. The cytological details of cataphyll initiation are identical to that of needle initiation; however, the two primordia can be distinguished very early on the basis of their shape and direction of growth. After needle initiation the stem apex becomes inactive, is crowded to one side, and eventually disappears as the base of the needle enlarges. The results of the present work are discussed in relation to earlier conflicting interpretations regarding needle initiation and the subsequent existence of the dwarf‐shoot apex ofP. monophylla.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05972.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

Forty‐two morphological and eighty chemical (phenolic) characters were employed on a numerical taxonomic study of the genusPlatanus. Ten taxa were used for morphological study, and nine were available for chemical study. UPGA was employed for cluster analysis; correlation coefficients served as a measurement of the similarity between each OTU‐pair. Comparison was made for phenograms and graph diagrams of nine taxa based on morphological characters with those based on chemical characters. It has been found that the two agree with each other in many respects. Correlation coefficient between similarity matrices based on morphological and chemical characters is 0.573. The result generally supports the belief that taxa closely related on morphological grounds are similar biochemically. A systematic consideration of the genus has been made, based on the information available.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05973.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

The morphological sequence of the twelve chromosomes around the ring as worked out by Sax is reaffirmed with slight corrections of the centromere position on three chromosomes: Aa, fA, and Dd. Adjacent distribution was found in 53/120 MI PMC (44.2%). Ring‐position analysis was achieved in 34 of the 53. There were 127 chromosomes and 66 arm‐pairs involved in adjacent distribution in these 34 MI PMC. Adjacent distributions occurred at random among the twelve chromosome positions and among the twelve arm‐pair positions. There were eleven instances among the 66 arm‐pairs (16.7%) of adjacent distribution despite free ends due to chiasma failure. Up to four consecutive chromosomes may pass to the same pole. Not all cells with 6–6 distribution are genetically balanced. Distribution of 7–5 occurred in 24/120 AI PMC (20.0%). Another nine (7.5%) in the same sample had one or more lagging chromosomes. At MI, three PMC had 8–4 distribution, but none such were seen at AI.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05974.x

出版商:Wiley    

年代:1973

数据来源: WILEY