摘要:

Unialgal cultures of the macroscopic, vesicular, coenocytic gametophyte (Halicystis parvulaSchmitz) ofDerbesia tenuissima(DeNotaris) Crouan fr. were grown under various environmental regimes to elucidate the cytology of gamete formation and the factors controlling synchronous gamete formation and release. No synchrony of nuclear division was observed in vegetative plants or during the early stages of gamete formation. In the later stages of gamete formation in plants in a light‐dark cycle, nuclear divisions within any gametangium were synchronous, and the stages of gamete formation were synchronous for the population. This synchrony was not as great for plants in continuous light. Gametes of plants in a light‐dark cycle were released explosively immediately following the dark‐to‐light transition. Release was random and much less forceful for plants in continuous light. After a certain stage of gamete formation, gamete release was timed to occur after a particular interval of darkness, but release could be triggered by light during the last portion of this interval. The length of the dark interval was shorter for male plants than for females, but the period of light sensitivity was longer for females. Formation of gametangia by series of isolated plants was also synchronous and sometimes periodic under certain conditions. Intervals between gametangia on the same plant varied from 2 to 14 days but were usually 4 or 5 days (unlike plants in nature, which show a bi‐ or tri‐weekly periodicity). Male and female plants did not differ in synchrony or periodicity. Different media affected the number of gametangia formed over a period of time but not the synchrony of formation. Under some conditions changing the medium had a stimulating or synchronizing effect. Non‐repeated temperature changes also synchronized gamete formation. Optimum temperature for continued gamete formation was about 21 C. Regular daily light and temperature variation together maintained synchronous and periodic gamete formation in populations of isolated plants. Reproduction diminished and became less synchronous at constant temperature either in continuous light or under a light‐dark schedule, although in the light‐dark regime steps in the formation of any given gametangium remained synchronous with the light‐dark cycle. Length of times between gametangial formation on individual plants showed a tendency to occur in multiples of the usual period lengths; e.g., plants sometimes tend to “skip” intervals, thus maintaining the synchrony of the population. These results suggest that interaction between daily environmental cycles and an endogenous physiological cycle may maintain periodic reproduction.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb06937.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Under improved environmental conditions the average rate of elongation of the rhizoid cluster was 5.2 mm/day in the first 3 days. The rate decreases thereafter and is close to zero around 5–6 days after initiation. The elongation, like that of the rhizome, is chiefly by means of “tip‐growth.” The presumptive site of the initiation is 1.3–1.7 mm from the rhizome tip. Under present experimental environment, the presumptive time of the initiation was mainly at 1 to 3 hr after the beginning of the light period. Initiation in the dark period was less frequent, and little or no initiation in the middle and later parts of the light period was observed. The average plastochron of the cluster was 0.91 day. The rate of elongation of the rhizoid cluster was less variable than that of the rhizome. Hence, the slope of calculated regression line from the plot, the cluster length vs. its distance from the rhizome tip, is steeper when the rhizome grows slower (4.9–5.8 mm/day) and less steep when the rhizome grows faster (7.3–8.9 mm/day). In spite of some variation in the slope of the regression line, the intersection between the line and X‐axis remains about the same. The application of information on the presumptive site and presumptive time of the rhizoid cluster initiation to a developmental study of micro‐events taking place prior to the morphological differentiation is proposed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb06938.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Seeds of aquatic and semiaquatic angiosperms were fed to two representative waterbirds: killdeer (Charadrius vociferus) and mallard ducks (Anas platyrhynchos). The viability and maximum period of retention for seeds recovered from the droppings were determined. Results indicate that resistance of the seeds to avian digestive processes depends both upon the nature of the seed coat and the species of bird through which they pass. Periods of maximum retention, greater in killdeer than in mallard ducks, were much longer than had previously been supposed. Plants with highly resistant seeds are for the most part of wide geographic distribution suggesting that the extensive range of many aquatic plants can be accredited, at least in part, to their adaptation to internal transport by birds.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb06939.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Immature seeds ofMelampyrum lineareDesr. have very high germination percentages and dormancy is induced in a variable fraction of the seed crop during ripening. Correlated with this is the endogenous gibberellin‐like activity which is found in considerable amounts in immature seeds, less in batches of ripe seeds, and is not detectable in batches containing only dormant seeds. For germination dormant seeds require activation followed by cold storage. In the laboratory activation is produced by allowing moist, dormant seeds to respire freely for several weeks at 20 C, or by treatment with exogenous GA3. Dormancy appears to be most directly related to inability of the embryo to hydrolyze the thickened, mannan‐containing endosperm cell walls. Embryos excised from dormant seed can be grown on agar enriched with whole macerated dormant seeds or with the ethanol‐extractable materials from these (mostly sucrose and a glycoside). However, dormant seed material does not support growth when extracted to remove benzene‐ and ethanol‐soluble materials.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb06940.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Moss protonemata ofPhyscomitrium turbinatumwere grown on mineral nutrient agar in culture tubes under various controlled conditions. By use of the described system individual cells of the protonema were discernible in situ and buds could be detected at the one‐cell stage (initiation) and observed throughout their development. Buds normally arose by differentiation of a lateral filament near the apex of a growing caulonemal (heterotrichous) strand. Other modes of origin were erratic. From various other observations we conclude that the most pertinent morphological assays in studies of bud differentiation are growth of single caulonemal strands and the time they require to initiate a bud. A time course for bud development from the one‐cell stage through the stage of leaf expansion is presented. At 26 C, 2 days elapse between these stages. From the time course, the time of bud initiation could be estimated with a probable accuracy of ±2 hr with only daily observations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb06941.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Clonal protonemata of the mossPhyscomitrium turbinatumwere grown on a mineral nutrient, sucrose, agar medium under a wide range of incandescent light intensity, temperature and photo‐period conditions. Shoot‐bud differentiation was assayed as the amount of calendar time and total hours of illumination required between inoculation (protonemal inoculant) and initiation (the one‐celled stage) of the first bud in the colony. There was no correlation between bud initiation and amount of protonemal growth. When temperature was not limiting, bud initiation occurred upon giving a requisite light dose regardless of how the light was divided into photoperiods over various durations of calendar time. We interpret this “cumulative light‐dose” effect to mean that budding was dependent upon a threshold level of some morphogenic substance which was synthesized in strict accordance to light dose and was held in store over dark periods. The relationship between time required for bud initiation and light intensity showed that the rate of synthesis of the substance was linear with the log of light intensity in the range from 30–715 ft‐c. Experiments at low temperature (16 C) indicated that the light reaction was dependent upon substrates provided by dark reactions. Accumulation of the proposed substance was also dependent upon the sparing action of carbohydrate which could be provided either by optimal photosynthesis or exogenous addition of sugar. In the absence of added sugar time required for budding increased in direct relation to increasing proportions of dark periods or decreasing light intensity below the optimal level.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb06942.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Ascocarpic studies of the ontogeny ofLophodermium nitensdisclosed a type of development unlike that of all other species of Hypodermataceae occurring on conifer needles. For this reason the centrum ofL. nitensis designated as Type III and is compared with Type I (Gordon, 1966). BecauseL. nitensproduces its ascocarp in several tissues of various species of pine, the ontogeny of ascocarps in different locations is discussed and illustrated. The most significant ontogenetic feature of the ascocarp ofL. nitensis a layer of hyaline cells in the primordium; this layer is meristematic and gives rise to all subsequent structures of the centrum.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb06943.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Cells in the interior of susceptible oat roots treated with the disease‐inducing agent victorin exhibit many of the ultrastructural features which characterize the epidermal or outermost root cap cells of untreated roots. An increase in electron density of cell walls fixed in permanganate is the first effect of victorin seen in the root interior. Other early victorin‐induced changes are formation of enlarged, densely stained vesicles by the Golgi apparatus and organization of the endoplasmic reticulum into roughly parallel profiles. All of these features are characteristic of untreated epidermal cells. Victorin also induces the formation of large numbers of lomasome‐like wall lesions and causes a marked increase in the number of nearly spherical, membrane‐bounded structures tentatively identified as spherosomes. Similar lomasome‐ and spherosome‐like structures are much more abundant in the outermost cells of the root cap than in other regions of untreated roots. This suggests that these structures may be characteristic of cells destined to undergo disintegration. Victorin‐induced lesions appear to arise within the cell wall as the result of an activation of wall‐degrading enzymes. An early change which makes the unit structure of the plasma membrane visible over extended areas may account for victorin‐induced changes in permeability. Disrupted plasma membranes and swollen mitochondria are found only in cells heavily damaged by victorin. Many of the effects of victorin resemble those of calcium deficiency and calcium is known to suppress victorin‐induced disease symptoms. This suggests that calcium nutrition may play a role in the pathological changes induced by victorin.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb06944.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

With the inflorescence removed, intercalary growth can be maintained in the scape ofGerbera jamesoniiby application of gibberellic acid (GA, gibberellin A3) or indole‐3‐acetic acid (IAA); the latter usually promotes more rapid and greater elongation than the former because of a greater effect on older tissues. Simultaneous application of the two substances, even when both are at optimal levels, promotes more rapid elongation than either substance alone; in fact, the rate of elongation may equal that of the intact scape. In decapitated scapes (receptacle and involucral bracts removed with the inflorescence), GA and IAA promote cell elongation with reduced or no cell division. In deflowered scapes (receptacle and involucral bracts intact) both GA and IAA promote cell division, as well as cell elongation, so that the pattern of scape elongation is nearly the same as that for intact scapes. Apparently the bracts and receptacle contribute something required for cell division which acts in concert with GA and IAA. Deflowered and decapitated scapes elongate at nearly the same rates initially; thus the rate of elongation does not depend on cell division. The ultimate length of the scape is dependent on cell number and, hence, cell division, since deflowered scapes attain greater lengths than those that are decapitated.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb06945.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Vegetative propagation and vegetative dispersal ofOxalis cernuawere studied.O. cernuais a bulbous dicotyledonous plant. The shoot of a grown plant is divided into two distinct parts: a vertical stem growing upwards and bearing the feeding roots, and a rootless horizontal thin stem. This last is pulled by means of a large contractile root and carries along with it a series of small buds, which form new bulbs at the end of the season. Several new bulbs are formed along the vertical shoot as well. Thus, the propagation bulbs ofO. cernuadisperse along two axes, which are at right angles to each other.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb06946.x

出版商:Wiley    

年代:1968

数据来源: WILEY