摘要:

Some Onagraceae are characterized by quite low pollen‐ovule ratios. We suggest they are an evolutionary response to highly efficient pollination, mediated through viscin threads, which hold large numbers of pollen grains together, and by stigmas, which are large relative to the area of the pollinator over which the pollen is spread. The pollen grains of some Leguminosae are joined by “exinal connections” which are chemically and morphologically similar to viscin threads. In the legumes the area of the stigma is small relative to the area of pollen on the pollinator and pollination is facilitated by short connections which hold small numbers of pollen grains together.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06295.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

A G2 Factor present in cotyledons ofPisum sativuminfluences several developmental events in roots. G2 Factor present in dry seeds (cotyledons and radicles) is transported to roots after germination and promotes cell arrest in G2 in about 35% of all root meristem cells. Present evidence suggests the G2 Factor promotes cell arrest in G2 only in cells that undergo normal cell differentiation (arrest) because the proportion of cells labeled with3H‐TdR after 16 hr does not differ among both seedlings or excised roots in the presence or absence of this substance. In this manner, trigonelline differs from chalones of animal tissues that usually suppress cell proliferation by cell arrest either in G1 or in G2. Experimental results suggest that cortex cells and not cells of vascular tissues in mature root tissues (20–22 mm from the meristem) are influenced by G2 Factor. Other recent publications indicate that the G2 Factor is trigonelline (N‐methyl nicotinic acid) and concentrations of synthetic trigonelline from 10−5to 10−7mare effective in promoting cell arrest in G2 in one of the G2 Factor bioassays.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06296.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

Spermatozoid‐forming cells ofColeochaete scutatawere found in packets of four arranged in concentric internal bands. Spermatozoids, which occur singly in antheridial cells, are spherical to ovoid, approximately 7 μm long by about 3.9 μm wide. As compared to relatively unspecialized zoospores, male gametes undergo a number of specialized cellular changes during development. The spherical nuclei and cytoplasm of mature spermatozoids are increased in density. Posterior plastids are reduced and contain large starch grains. Many small mitochondria are clustered near the cell anterior. The plasmalemma is covered with a layer of flattened, diamond‐shaped scales, while body scales of zoospores are pyramidal. The two flagella of both zoospores and spermatozoids are covered with flattened, diamond‐shaped scales and hairs. The spermatozoids contain an anterior multilayered structure (MLS) structurally similar to, though smaller than, the MLS observed in zoospores. An asymmetrical cytoskeleton consisting of a band of 30–45 microtubules extends from the MLS down one side of the spermatozoid close to the plasmalemma. An immature MLS was observed in an early stage of spermatozoid development. The finding of an MLS and asymmetrical cytoskeleton in specialized male gametes as well as relatively unspecialized zoospores ofColeochaetestrengthens assumptions of homology between MLSs of green algal reproductive cells and those found in flagellated spermatozoids of archegoniate plants. The structure of the spermatozoid ofColeochaetesupports the hypothesis that this alga may be relatively close to the phylogenetic line which led directly to archegoniates.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06297.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

Shoot apical meristems of jack pine were examined weekly during the first 8 weeks post‐germination with light and electron microscopy. Most of the storage lipids were utilized by the end of the 2nd week. A few lipid bodies, possibly high in phospholipid content, remained in the apical initials and central mother cells and, during the 3rd week, gave rise to vacuoles via lamellar or myelin‐like structures which were first seen on their periphery. The inter‐lamellar spaces enlarged and eventually a vacuole was formed. At 5 weeks, elongate and spherical osmiophilic inclusions, presumably lipid, were found in the endoplasmic reticulum. Lipid bodies, visible with light microscopy, began to accumulate in the apical initials and central mother cells in the 6th week.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06298.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

T. latifoliagrows along most of the shoreline of Par Pond, a cooling reservoir for the reactors at the Savannah River Plant in Aiken, South Carolina. A thermal gradient exists because of the movement of hot water from one end of the pond to the other. This study was undertaken to determine the biochemical and morphological effects of temperature onTypha latifoliaclones originating from different ends of this thermal gradient. The data indicated that both “hot” and “cold” end plants react similarly to temperature. Forty‐eight rhizome plants from both ends of Par Pond were transplanted into tanks at 20 C and 30 C. Total levels of malic dehydrogenase activity, proportions of mitochondrially bound MDH and growth rates were significantly different in plants grown in the two tanks, but no significant differences were observed within each tank between individuals from the “hot” and “cold” end. The relation of these results to hypotheses concerning quantitative strategies of enzyme adaptation are discussed in the paper.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06299.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

A callus or cup at the spikelet base inEriochloais a diagnostic character for this genus. In an investigation ofEriochloaand related genera, the callus epidermis of 19 taxa ofEriochloaand the basal portion ofAxonopus, Brachiaria, Digitaria, Leptoloma, andPanicumspikelets were examined with a scanning electron microscope.Eriochloataxa were divided into three types based on callus epidermal characteristics. The callus ofE. polystachyamore closely resembled the reduced first glume in other panicoid genera than the callus in other taxa ofEriochloa. Bicellular microhairs, silica bodies, and interlocking long cells support the concept that the callus inEriochloais in part a remnant of the first glume.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06300.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

Anatomically preserved specimens of a woody lycopsid showing the transition from the stem to the rooting region are described from the Upper Pennsylvanian Duquesne Coal of Ohio. Specimens have exarch protosteles that are apparently medullated at distal levels and exhibit abundant secondary xylem. Cortical tissues accompanying the stems have periderm, and show leaf bases or cushions. Although features of the stems are compatible with those of the arborescent Lepidodendrales, the plants have a rounded cormose rooting region, rather than the much‐branched and elongated stigmarian system usually associated with the order. Specimens of this type expand our knowledge of the diversity among Paleozoic lycopsids and document the occurrence of representatives with anIsoetes‐like base in Pennsylvanian strata.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06301.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

Immature sieve elements of pennycress(Thlaspi arvense, Brassicaceae) were studied with the electron microscope in connection with studies on virus‐infected plants. Immature sieve elements contained cytoplasm rich in organelles and other components: endoplasmic reticulum, dictyosomes and associated smooth and coated vesicles, mitochondria, plastids, ribosomes, microtubules, microfilaments, vacuoles, and nuclei that were sometimes lobed. Tubular P‐protein (phloem protein) and one to three granular P‐protein bodies also were present in the cytoplasm. Coated vesicles may be involved in formation of the granular P‐protein body and in some aspect of cell wall development, for in the latter case, they were often seen united with the plasmalemma. The association of coated vesicles with the P‐protein body is discussed with reference to proposed concepts of the origin and function of these vesicles.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06302.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

The volumes and dimensions of shoot apical meristem zones were determined for 21 species in 10 genera of the Cactaceae. If the volumes of the central‐mother‐cell zone (CMCZ), the peripheral zone (PZ), and the pith‐rib meristem (PRM) are expressed as percentages of the total volume of the corpus, then they are remarkably constant (CMCZ = 11.1% of the volume of the corpus, PZ = 61.2% and PRM = 27.1%) regardless of the relative size of the apical meristems. The relative volume of the tunica decreases, however, as the whole apex increases. The zones have variable shapes, and whereas the PZ and PRM are always trapezoidal in longitudinal section, in apices with large volumes, these zones have a flatter, more flaring shape than they have in smaller apices. Thus large apices are flatter and less hemispherical than are small apices. The CMCZ, however, maintains a constant shape and is always relatively hemispherical regardless of its volume. A hypothesis that relates all of these shape and volume relationships as an integrated growth sequence is proposed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06303.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

Experiments were conducted to examine whether leaf adaptation to light inFragaria virginiana(Rosaceae) was determined by peak photon‐flux density or by total quanta received during the day. Leaf structure and apparent photosynthesis rates were similar under environments where total energy received was the same even though peak photon‐flux density was different. When peak photon‐flux density was held constant and total quanta varied, significant differences were noted in apparent photosynthesis, leaf thickness, specific leaf weight, mesophyll cell volume, and Ames/A ratio. High total quanta produced high‐light or sun‐type leaves even at relatively low peak intensities. Thus, total light energy received during the day has a greater influence on leaf adaptation to light than does peak photon‐flux density.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06304.x

出版商:Wiley    

年代:1979

数据来源: WILEY