摘要:

Reproductive adaptation to photoperiod is diverse among desert populations ofXanthium. Chihuahuan Desert populations require dark periods of 9.5–10.5 hr for reproduction, and Sonoran Desert populations require 9–10.5 hr. Many Chihuahuan populations from western Texas two weeks from sowing need only 10 cycles of 11‐hr nights to produce 100% flowering, but Sonoran populations from western Mexico four weeks from sowing need 18 cycles or more. Some Sonoran plants produce buds only at a cooler temperature program, 24–15 C, but Chihuahuan plants produce them more readily under the warmer program, 30–24 C. Chihuahuan plants that were germinated under 11‐hr nights and four different temperature programs were induced to flower in each condition. Differences in photoperiod and ripeness‐to‐flower (maturity) responses were also demonstrated under natural day lengths in central Texas. Although desert populations occurring at approximately the same latitude in either the Chihuahuan or Sonoran Desert are exposed to similar day lengths, each population may be adapted to different photoperiod cues that maximize its utilization of the local growing conditions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05940.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

Extracts ofMarchantia polymorphacontain substances which, in vitro, strongly inhibit or enhance indoleacetic acid oxidation by both horseradish peroxidase and an IAA oxidase enzyme fromM. polymorpha. The extracts can be partially freed of such activity by dialysis, passage through a column of polyvinylpyrrolidone powder, or extraction with an anion exchange resin. Chromatographic separation of the extract revealed the presence of four as yet unidentified phenolic compounds. Two inhibited and two enhanced IAA oxidase activity. Inhibitory activity was not destroyed by horseradish peroxidase in the absence of IAA. The level of these compounds in various regions of thallus was measured. Inhibitors were present throughout the tissue, with some localization in the basal and apical areas; there was an acropetal gradient of increasing cofactor concentration.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05941.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

Stigmaria stellataGoeppert is a lycopod underground system occurring in Upper Mississippian and equivalent age rocks of Europe and North America. This taxon has previously been based on impressions exhibiting radiating ridges and furrows around each lateral appendage scar and numerous polyhedral projections on the remainder of the axis. Anatomically preserved specimens from the Chester Series (Upper Mississippian) of Illinois reveal that the distinctive surface pattern of this species results from polyhedral wedges of thick‐walled cells in the outer cortex. Decortication produces a smooth outer surface that is indistinguishable from that of the much more abundantStigmaria ficoides. The structure ofS. stellatais quite similar to the structure of other petrified stigmarians, but the following are some of the anatomical characters that distinguish it: (1) presence of abundant polyhedral wedges of thick‐walled cells in the outer cortex; (2) absence of secondary cortex; (3) very tall rays associated with appendage traces that remain confluent with the secondary xylem to its outer margin; (4) the absence of a connective in the lateral appendages. The anatomical characters ofStigmaria stellataconfirm it as a taxon of at least specific rank.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05942.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

Gas exchange studies were carried out onArtemisia tridentataduring the course of a growing season using microclimatically controlled cuvettes and infrared gas analysis. A definite seasonal pattern of net photosynthesis emerged. This pattern was influenced by the interaction of four major factors: plant water potential, leaf temperature, irradiation, and stage of phenological development. In spring and early summer, when plant water stress was minimal, photosynthesis rate was mainly correlated with leaf temperature and irradiation. During mid and late summer, increased plant water stress and phenological changes assumed at least equal importance with temperature and irradiation in limiting net photosynthesis. Indeed, plant water potential, mainly through its influence on stomatal aperture, rs‘, was probably the single most important factor influencing assimilation rate of this species on a seasonal basis. However, variations in mesophyll resistance to CO2flux, rm‘, in response to temperature, water stress, or phenological changes also were involved. Sagebrush photosynthesis under field conditions was highest in late May and early June, and declined thereafter, minimum rates occurring in August during the driest period. Optimal temperatures for net photosynthesis were higher later in the season, indicating a change in gas exchange capacity more suitable to the warmer temperatures later in the season.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05943.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

This paper reports light and electron microscope observations of changes in the walls of cortical cells in the laminar abscission region of red kidney bean (Phaseolus vulgarisL.). In intact plants two or three rows of cells comprise the abscission zone. Pectic substances are not present in the walls of these cells when wall breaks occur. The separation cavity involves breaks in both radial and longitudinal cell walls. In ethylene‐treated explants pectic substances are present in the cell walls when breaking occurs. The separation cavity involves breaks in longitudinal walls only, and breaking is confined to a single row of cortical cells. Prior to cell wall break the plasma membrane frequently invaginates. In intact plants this may be associated with plasmolysis and with the formation of secondary vacuoles. In ethylene‐treated explants it may also be related to plasmolysis. At the time of cell wall break many unidentifiable inclusions of varying sizes and shapes are present in the cell wall region. Chloroplasts and mitochondria are structurally altered but recognizable in the cell at the time of wall break. Plasmodesmata are frequently observed in abscission cells and may be structurally elaborate. The observations of the nature of cell wall changes during abscission in ethylene‐treated material fail to confirm physiological studies of other workers suggesting that pectin dissolution is necessary and may be sufficient for formation of a separation layer.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05944.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

Comparative cytological and histological studies during embryogenesis of seeds from 2x X 2x and 2x x 4x crosses indicate that the ratio of ploidy level between embryo and endosperm is the most important factor affecting the course of seed development. The crosses produced seeds with the expected ploidy relationships between embryo, endosperm, and maternal tissue of 2:3:2 and 3:4:2 as well as the anomalous relationships 3:5:2, 4:6:2, and 6:10:2. All but 3:4:2 resulted in normal, germinable seeds. The ploidy level of the maternal tissue in relation to that of the embryo or endosperm did not appear to have any effect on seed development. About 92–99 % of seeds from 2x x 4x crosses containing triploid embryos with tetraploid endosperm aborted at different stages of embryogenesis. The abortion in all cases was preceded by abnormalities in the tetraploid endosperm. It is postulated that the unbalance of chromosome number between embryo and endosperm disturbs physiological relationships between these two tissues, leading first to the abortion of the endosperm and then of the embryo.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05945.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

Schopfiastrum decussatum, a monostelic pteridosperm, has been recovered from Middle Pennsylvanian age coal balls from six localities within the Illinois Basin. Additional features of stem anatomy include the presence of horizontal sclerotic plates in the inner cortex, secretory ducts in the inner and outer cortex, and adventitious roots. The primary xylem is interpreted as bilobed, emitting massive leaf traces in a distichous manner. Five orders of frond members are described, including pinnules. All orders of the frond contain secretory ducts and tissues characteristic ofSchopfiastrumstems. The rectangular, bilobed protostele, and method of leaf trace origin indicate thatSchopfiastrumis more closely related to certain lower Carboniferous seed ferns than to contemporary Pennsylvanian pteridosperms.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05946.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

Yearly ring‐width indices were determined forQuercus stellataandQ. marilandicain central Oklahoma for the period 1892–1971 and were used as dependent variables in correlation analyses with corresponding series of previous growth rates and various precipitation totals as independent variables. Results of multiple correlation show that approximately 60% of the variance in ring indices of both species can be accounted for by precipitation and previous growth rates. Simple linear correlation analysis of precipitation data shows that the ring index value for a year is significantly correlated with rainfall in the current spring and in the previous summer.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05947.x

出版商:Wiley    

年代:1973

数据来源: WILEY

摘要:

The genusMetrosideros(Myrtaceae) is an abundant and taxonomically confusing component of the vegetation throughout much of its range. In the southern Pacific, from the New Hebrides eastward to the Society and Tuamotu Islands, the genus is represented by one variable species,M. collina(J. R.&G. Forst.) A. Gray, in which three widespread varieties seem to merit recognition. An attempt is here made to clarify the nomenclature and inter‐relationships of these varieties. Additionally, two local endemics are related to theM. collinagroup—M. gregoryiChristophersen in Samoa andM. ochranthaA. C. Sm. (sp. nov.) in Fiji.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1973.tb05948.x

出版商:Wiley    

年代:1973

数据来源: WILEY