摘要:

Ultrastructural and histochemical changes during intracapsular cell differentiation in the premeiotic sporophyte of the liverwortSphaerocarpos donnelliiAustin were studied. From an initially undifferentiated meristematic tissue, spore mother cells and nutritive cells become differentiated. The first indications of ultrastructural differentiation into two cell types are the accumulation of lipid within spherosomes and the occurrence of plastid tubules in the presumptive spore mother cells. Once differentiated the two cell types are clearly distinguishable on the basis of cytoplasmic vacuolation, stored food reserve, and cell and nuclear size. The mature spore mother cell contains many spherosomes, small vacuoles, starch‐containing plastids, and a large central nucleus. The mature nutritive cell, on the other hand, is extremely vacuolate and contains large, starch‐filled plastids, a few spherosomes, and a small nucleus. A previously undescribed type of cell was observed in developing sporophyte capsules. This cell is located peripherally in the capsule and degenerates during differentiation of spore mother cells and nutritive cells.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14083.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

Analyses of chromosome pairing behavior in fern hybrids, as evidenced by the degree of bivalent and/or univalent formation at meiotic prophase, have frequently been employed in studies of evolutionary relationships within polyploid fern complexes. Pairing is often seen to involve genomic numbers of chromosomes. Many examples exist, however, that indicate pairing on subgenomic levels. If this type of behavior is not recognized in analyses of F1hybrids and their polyploid derivatives, interpretations of evolutionary relationships based upon pairing behavior may be misleading. Contrary to some views, sterile triploid hybrids possessing less than three distinct genomes may play a significant role in the formation of reticulate polyploid complexes. This possibility must be considered in interpretations of these complexes. With these factors in mind, the AppalachianDryopteriscomplex has been reinterpreted. The reinterpretation provides explanations for several unexplained inconsistencies in previous interpretations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14084.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

The floral and foliar nectaries ofTurnera ulmifoliaare specialized and are representative of others found in the Turneraceae. The foliar and floral nectary systems must be treated independently. Foliar nectaries are organized into a definite structure (composed of a base, rim, secretory tissue, modified epidermis) and are supplied with vascular tissue composed of both xylem and phloem. Nectar from foliar nectaries contained equal concentrations of glucose, fructose, and sucrose. Floral nectaries are an integral part of the basal portion of each filament. The nectariferous tissue is not supplied with vascular tissue and secretion lasts only a few hours. Nectar from these staminal nectaries yielded a sucrose‐dominant nectar containing also fructose, glucose, an unknown, and a trace amount of melezitose. Observations of flowering confirmed the reported short duration of the individual flowers.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14085.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

The morphology of plastid starch grains from several succulent and nonsucculent species ofEuphorbiawas examined in parenchyma and in non‐articulated laticifiers. Several classes of grains were identified: small oblong‐round, rod, somewhat osteoid, osteoid, lobed osteoid, discoid, and round grains. Parenchyma possessed only small oblong‐round grains, whereas grains of different morphology were present in laticifers. Different species of this genus can be characterized by the morphology of the large, or mature, starch grains present in the laticifer. The rod‐shaped grain, which was somewhat wider at the midregion than at the ends, was present in several nonsucculent forms,E. terracina, E. pulcherrimaandE. heterophylla.The somewhat osteoid grain was represented by the succulent speciesE. viguieri, E. milii, andE. mauritanica, where the mature grains developed somewhat enlarged ends. Grains with much enlarged ends were represented in the succulent species ofE. abyssinica, E. pseudocactus, andE. tirucalli.Alteration of the pattern of starch deposition in which several lobes were formed at the ends of the grain has given rise to a lobed osteoid class (E. inconstantia). Lobes also may be formed with greater frequency along the midregion of the grain in this than in other species.Euphorbia lacteahad the most complex grain in which lobing was frequent at the ends as well as along the midregion, resulting in a large discoid grain. Subclasses in which grains differed significantly in length between species were evident in all classes containing several species. The average length of grains in any subclass was similar for subclasses between the classes. The study suggests that the elongated grain of the laticifer was derived from the round or oblong grain present in the more primitive parenchymatous cell. Progressive changes in the pattern of starch deposition have given rise to osteoid and discoid grains of increasing morphological complexity which is interpreted to represent trends in laticifer evolution between different species ofEuphorbiaas reflected by subtle changes for starch deposition within the plastids of this cell.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14086.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

This report assembles and pictorially presents observations on the timing of relatively uniform and well‐defined developmental events in the cotton flower and its component parts. The first floral bud occurs on the 7–9th node approximately 35–40 days postemergence; 20–25 additional days elapse until anthesis. Floral parts are morphologically well defined by two weeks preanthesis. In about 85 % of the flowers the basal, abaxial surface of two of the three bracts contains an outer involucral nectary; occasionally, none, one, or three nectaries are found. The maximum rate of increase in floral bud length occurs during the 24 hrs preceding anthesis. Flower opening occurs at about daylight, although light is not required. Multipored pollen grains germinate in about ½ hr after deposition on the stigmatic hairs. Fertilization is accomplished, for most ovules, by the end of the first day postanthesis. Stomata are abundant, particularly at the chalazal ends of ovules. Fiber initials (epidermal cells of the ovule) begin their elongation phase on the morning of anthesis and are bounded by a thin primary wall. Areas of contrast (spots) observed through the scanning electron microscope are speculated to be organelles “seen through” the relatively amorphous fiber wall, which lacks extensive fibrillar orientation of cellulose. Fiber elongation ceases by about 24–28 days postanthesis, and by 50–70 days postanthesis fibers are mature and exhibit a thickened secondary wall and spiral twisting. Concomitant with the time of fiber maturity, the ovary wall splits and opens along locular suture lines.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14087.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

Twenty trisomic plants found in the progeny 3x x 2x crosses inSolatium chacoenseand their F1trisomies obtained by 2x + 1 X 2x crosses were studied with respect to their fertility and cytology. The female transmission of the extra chromosome in the trisomics varied from 2 to 60 %. The transmission frequencies of F1trisomies were similar to their parent trisomies in most of the lines. The transmission through the pollen ranged from 0 to 20 %. Female and male fertility of the parent trisomies was high. They produced an average of 37 seeds per pollination as the female or as the male parent. The F1trisomies produced about half the seed set of their parent trisomies. The extra chromosomes of six trisomies were identified by pachytene analysis. They were isochromosomes for the long arms of chromosomes I, IV and IX and the short arms of IV, IX and XII. Chromosome morphology of the extra chromosomes in pachytene stage was described. A chromosome association of 12 II + 1 I was found in 66 % of the cells at MI. About 29 % of the cells had one trivalent and 5 % had three or five univalents. The frequency of trivalent formation was not affected by the length of the extra chromosome. The possibility of univalent shift in secondary trisomies was discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14088.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

An immediate, marked response to small amounts of rainfall occurs inOpuntia basilaris, despite previous drought conditions. The effect of rainfall is upon plant water potential, which is the single most important parameter influencing stomatal opening, CO2assimilation, and organic acid synthesis. Nocturnal stomatal opening is initiated following rainfall, and stomata remain open during the daytime. Decreasing stomatal and mesophyll resistances correlate with increasing rates of nocturnal assimilation of14CO2. Photosynthetic rates of14CO2assimilation are low, despite high plant water potentials and low stomatal diffusion resistances. The decreased mesophyll resistances and increased rates of nocturnal14CO2assimilation correlate with the increases of nocturnal efficiency of water use and CO2assimilation. The diurnal efficiency of water use and CO2assimilation is lower than the nocturnal gas exchange efficiency values.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14089.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

Excised shoot apical meristems ofPicea abiesseedlings grow and develop primordial leaves when cultured on Millipore (mixed esters of cellulose) filter membranes lying on a simple, defined medium gelled with agarose. When the cultures are removed from the membranes, each leaves a spot of altered light transmission, spectral characteristics, hygroscopicity, and chemical reactivity. These spots are the manifestation of deposition in the membrane pore space of polysaccharides, lignin‐like components, and probably other substances. Deposition of water‐insoluble, Schiff's reagent‐positive substances can be detected in the filter membranes after only 3–6 hr exposure to a meristem and continues for 10–15 days or longer. Precursors of the insoluble deposition materials can diffuse through at least nine layers of Millipore membrane before deposition at a site remote from living cells. Placement of a dialysis membrane between the meristem and the Millipore membrane prevents detectable deposition in the latter. The observations are consistent with the hypothesis that apical meristems can synthesize and export mobile precursors of cell wall components as well as any substances necessary to promote their condensation or polymerization into insoluble materials at remote sites. The system may be useful in studying synthesis of cell wall components and investigating the functional role of growth regulators in shoot apical development.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14090.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

Plant growth inhibitors, which are known to exert synergistic effects on herbaceous vegetation, were isolated and quantified from the soils under hackberry trees. Ferulic, caffeic, and p‐coumaric acids were isolated from the soils under hackberry trees collected in January, April, and September from 0–15 and 15–30 cm soil depths. Seed germination bioassay indicated considerably higher phytotoxicity levels of individual plant growth inhibitors in January and April soils, and this toxicity level was more drastic when inhibitors were applied accumulatively. Individual phytotoxins extracted from soil in September were not very inhibitory to seed germination of selected test species; however, accumulative effects were still allelopathic to seed germination. Toxicity levels of individual compounds may reduce or disappear in a given time, but the combined action of these chemicals would still be toxic in croplands or in natural communities. Ecological implications of allelopathy in terms of soil‐plant interaction are discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14091.x

出版商:Wiley    

年代:1975

数据来源: WILEY

摘要:

Seed dormancy and its ecological aspects were investigated inIsanthus brachiatus, a summer annual plant of limestone outcrops in southeastern United States. Freshly matured seeds are dormant and exhibit physiological polymorphism with respect to the conditions necessary to overcome dormancy. Fifteen to thirty‐five percent of the seeds in a seed crop require only one stratification treatment and germinate the first spring following their dispersal in autumn. The remainder of the seeds require two, three, or more stratification treatments and thus do not germinate until after two, three, or more overwintering periods in the field. In those seeds that require more than one stratification treatment to overcome dormancy, the stratification periods must be separated by a “rest” period, which in nature corresponds to summer. The ecological significance of this type of seed dormancy mechanism inI. brachiatusis discussed in relation to adaptation to its habitat.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1975.tb14092.x

出版商:Wiley    

年代:1975

数据来源: WILEY