摘要:

The dormant axillary buds ofOpuntia polyacanthacan be activated by either cytokinins or gibberellic acid. Under the influence of benzylaminopurine (BAP), the axillary bud meristem increases greatly in size and becomes mitotically active. The primordia produced by the meristem develop as normal photosynthetic leaves. Gibberellic acid (GA) also causes the meristem to become mitotically active, but the meristem does not increase in size. The primordia produced under the influence of GA develop as normal cactus spines. Leaf‐producing meristems and spine‐producing meristems have the same zonation, despite the differences in size. The meristems are composed of a uniseriate tunica, a central mother cell zone, peripheral zone, and a pith rib meristem. The mitotic activity of each of the zones in the leaf‐producing meristem differs significantly from the mitotic activity of the corresponding zones in the spine‐producing meristem.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb13214.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

The discovery of numerous specimens of the monostelic pteridosperm genusMicrospermopterisin Pennsylvanian coal ball petrifactions from the Lewis Creek and What Cheer localities provides additional information about the anatomical and morphological variability within the genus. Specimens are now known up to 1.1 cm in diam that bear epidermal appendages in the form of variously‐shaped trichomes. The external surface of the stem is further ornamented by longitudinal flaps of cortical tissue. Petioles exhibiting a single C‐shaped vascular strand with abaxial protoxylem are produced in a 2/5 phyllotaxy. Large petiole bases that clasp the stem produce primary pinnae alternately. The presence of axillary branching appears similar to that reported inCallistopliytonandLyginopteris.Triarch to polyarch adventitious roots, some with secondary tissues, are produced at both nodal and internodal regions. Of the currently recognized monostelic seed fern genera,Microspermopterisis most similar toHeterangium.Information is presented that supports current ideas regarding the evolution of the gymnospermic eustele from protostelic Devonian ancestors.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb13215.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

Eleusine coracanassp.coracana(finger millet, eleusine) is widely distributed in Africa and India as a cereal. The crop is cultivated in diverse eco‐geographical areas. Over this range of distribution, eleusine displays high variability in vegetative, floral and seed morphology. The intent of this study is to establish correlations between morphology and distribution, and to determine the intraspecific taxonomy of the crop. Three eco‐geographical races were determined: (1) an African highland race which is cultivated in the East African highlands, (2) a lowland race which is grown in the lowlands of Africa and South India, and (3) an Indian race with its center of distribution in Northeast India. In addition to these basic races, an Indian highland type was identified. The African highland race is the most primitive from which the lowland race evolved. The latter race was subsequently introduced to southern India where a secondary center of diversity became established. The Indian race originated from the lowland race, while the North Indian highland type can be derived from either or both of the two basic races in India. This study indicated that natural selection played a major role in the evolution of the crop. Artificial selection, although significant, was restricted within the limits imposed on it by the ultimate adaptation of the races to their environments.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb13216.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

Flowers ofPolygalaare irregular, each having three small and two long winglike sepals, three petals, eight stamens, and a bilocular ovary. These flowers have been considered pentamerous, and placentation has been subject to various interpretations. Development and anatomy of flowers ofPolygala alba, P. lanceolata, andP. luteawere studied to see if evidence of pentamery and change in placentation could be found. These studies reveal no evidence of vestigial petals or stamens nor of vascular traces to organs that are missing in the three species studied. Neither are there abortive sporangia in the bisporangiate anthers. Observations on development of carpel primordia and on the vascular plan of mature carpels indicate that placentation is fundamentally parietal rather than axile. Speculation is offered as to the derivation of this type of placentation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb13217.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

Eoginkgoitesis a fan‐shaped, imparipinnate leaf with a short rachis and long petiole. It was first described from the Upper Triassic Newark Group of Pennsylvania by Bock who assigned the fossil to the Ginkgoales. The fossil has also been found in the Upper Triassic Chinle Formation in Utah and Arizona and in the Newark Group in North Carolina. Investigation of the well‐preserved specimens found in the Chinle Formation shows that the leaf has anastomosing venation, a marginal vein and paracytic (syndetocheilic) stomata. These characters indicate that the leaf is bennettitalean andEoginkgoitesis reassigned to the Bennettitales although its shape is perplexing.Eoginkgoitesmay be an important index fossil to the lower Upper Triassic (middle Carnian) rocks of North America.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb13218.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

The concept of a procambium‐cambium continuum was examined inPopulus deltoidesby following its development in serially sectioned bud and stem tissues. As in other species, the term cambium is used to refer to that part of the continuum associated with the formation of secondary vascular tissues; i.e., with secondary growth. However, that part of the continuum associated with the formation of primary vascular tissues is subdivided to facilitate interpretation of the consecutive stages of primary xylem differentiation. Thus, the procambium as envisioned by other authors is subdivided into procambium, initiating layer, and metacambium, all of which develop acropetally and in complete continuity. The procambium is derived from the residual meristem in the form of acropetally developing strands and traces. The initiating layer is represented by the first, tangentially separated, periclinal divisions that delineate the position of the prospective cambium. The metacambium is a later stage during which additional periclinally dividing cells unite the initiating layer into a tangentially continuous meristem within a trace bundle. After establishment of the initiating layer, the procambial trace is completely phloem dominated. Protoxylem differentiation begins in an originating center at the base of the leaf primordium and it progresses basipetally to form the protoxylem pole. Cells of the initiating layer do not contribute to the formation of either protoxylem or protophloem. However, those cells of the initiating layer directly opposite the protoxylem pole divide precociously and later differentiate to metaxylem, thus forming a radial file of protoxylem‐metaxylem elements. Protoxylem elements of lateral traces are longitudinally continuous with the protoxylem of their parent traces, whereas those of a central trace are longitudinally continuous with the metaxylem of its parent trace. Metaxylem is formed later than protoxylem and it is derived from the metacambium. Metaxylem does not form a continuous system with protoxylem of the same trace because of the different temporal and spatial origins of the two kinds of xylem. Rather, metaxylem is longitudinally continuous with secondary xylem of older traces below. An attempt was made to determine the functional significance of the pattern of protoxylem and metaxylem differentiation in relation to primary and secondary plant development.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb13219.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

The genusCampsis(Bignoniaceae), with one New World and one Old World species, is unusual among temperate plants in having five distinct nectary sites. Multiple nectaries occur at all four of the extrafloral sites (petiole, calyx, corolla, fruit), representing an advanced strategy for ant attraction. The morphology and anatomy of the extrafloral nectaries in both species are uniform for the petioles, calyces, and young fruits; those on the outer corolla lobes are of slightly different forms. The generalized structure consists of one layer of basal cells, and a one‐ to two‐layered secretory cup. Because of their small size, there is no vascular tissue in them. The large, vascularized (phloem only) floral nectary is an annular structure subtending the ovary.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb13220.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

The productivity and composition of two study sites in a southern Louisiana freshwater swamp were studied from October 1973 to November 1974. Net productivity was determined from measurements of litter‐fall, stem growth of woody species, and harvest samples of annual herbaceous understory. Annual stem growth was calculated from biomass estimates on two different dates. The annual increase in stem biomass was 800 g dry wt/m2for a bottomland hardwood site (BLH) and 500 g dry wt/m2for a baldcypress‐water tupelo site (CT). Litter‐fall was 574 g dry wt/m2/yr for BLH and 620 g dry wt/m2/yr for CT. Harvest samples within the two plots yielded 200 g dry wt/m2and 20 g dry wt/m2for BLH and CT, respectively. Minimum net primary production was calculated as the sum of the three: 1574 g dry wt/m2/ yr for BLH and 1140 g dry wt/m2/yr for CT. Maximum estimates of herbaceous production and insect consumption were made by using values from the literature. Estimated total net primary productivity was 1733 g dry wt/m2/yr for BLH and 1516 g dry wt/m2/yr for CT. Tree composition was determined by the point‐centered quarter method. Relative frequency, relative density, absolute density, relative dominance, and importance value (IV) were calculated for the tree species along each transect. In the bottomland hardwood area many woody species exist withAcer rubrumvar.drummondii(IV = 23.9) andNyssa aquatica(IV = 18.4) the most dominant. In the baldcypress‐water tupelo area, fewer woody species exist andTaxodium distichum(IV = 39.2) andN. aquatica(IV = 37.6) dominated. Comparison of productivity data from several southeastern swamps indicate that flowing water regimes tend to result in the highest swamp forest productivity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb13221.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

The anatomy and organization of the stem vascular system was analyzed in representative taxa ofNymphaea(subgeneraAnecphya, Lotos, andBrachyceras).The stem vascular system consists of a series of concentric axial stem bundles from which traces to lateral organs depart. At the node each leaf is supplied with a median and two lateral leaf traces. At the same level a root trace supplies vascular tissue to adventitious roots borne on the leaf base. Flowers and vegetative buds occupy leaf sites in the genetic spiral and in the parastichies seen on the stem exterior. Certain leaves have flowers related to them spatially and by vascular association. Flowers (and similarly vegetative buds) are vascularized by a peduncle trace that arises from a peduncle fusion bundle located in the pith. The peduncle fusion bundle is formed by the fusion of vascular tissue derived from axial stem bundles that supply traces to certain leaves. The organization of the vascular system in the investigated taxa ofNymphaeais unique to angiosperms but similar to other subgenera ofNymphaea.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb13222.x

出版商:Wiley    

年代:1976

数据来源: WILEY

摘要:

Cruciate dichotomous branching is a regular phenomenon in at least two species of cacti:Mammillaria perbellaandM. parkinsonii, and there is exomorphic evidence that it occurs in other species of this genus. The specimens examined showed no obvious changes in the phyllotaxy of the two shanks derived by dichotomy. In the ecologically and morphologically specialized Cactaceae, it is quite unlikely that dichotomous branching represents the retention of a primitive character. It is furthermore improbable that it is of taxonomic value above the species level.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1976.tb13223.x

出版商:Wiley    

年代:1976

数据来源: WILEY