摘要:

Transmission electron microscopy was used in an examination of dormant and germinating oospores ofPythium aphanidermatum(Edson) Fitzp. Predominant cytoplasmic components of the dormant oospore were a single, centrally located globule and numerous storage bodies surrounding the globule. The lipid nature of the central globule and storage bodies was indicated by the examination of Br2‐treated and untreated, fixed specimens. Three layers of the oospore wall were distinguished. During the early stages of oospore germination, the central globule developed incurvatures and became partially surrounded by vacuoles. The thick middle layer of the wall showed a change in staining properties and became thin in the region of germ tube emergence. Germlings incubated on corn meal agar differed substantially from those incubated in nutrient broth during the later stages of germination. The role of vacuoles and vesicles in the utilization of storage reserves during germination is discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06099.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

CO2and water vapor exchange studies of intact plants of black needle rush (Juncus roemerianusScheele) were conducted in an undisturbed marsh community on Sapelo Island, Georgia. The seasonal patterns of the light and temperature responses of net photosynthesis, transpiration, leaf diffusive conductance, water‐use efficiency and respiration were determined five times over the year. Internal resistances to CO2uptake were also evaluated. Net photosynthesis was highest in early spring, but declined only slightly through the year. A distinct and moderate temperature optimum of net photosynthesis was observed with decreasing rates above 30 C. Leaf conductances to water vapor were similar at all seasons and were high at cooler temperatures and decreased with increasing temperature. Transpiration was relatively high and constant during all seasons. The water‐use efficiency of photosynthesis was high below 25 C, but decreased sharply above that temperature. Dark respiration was relatively low. Seasonal changes reflected changes in leaf density. Decreasing stomatal conductances and increasing respiration rates reduced net photosynthesis at higher temperatures. The stomatal resistance increased and internal resistances to CO2uptake decreased over the year, but the total resistance remained constant. The internal resistance to CO2uptake was consistently higher than the stomatal resistance. These seasonal response patterns show thatJ. roemerianusis well adapted to the seasonal changes in ambient temperature and irradiance and other microenvironmental factors in the high marsh. These physiological characteristics permit this C3species to maintain a high productivity in a seasonally hot and stressful environment.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06100.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Juice vesicles of Valencia orange were grown on agar bases containing different concentrations of kinetin plus mineral and organic constituents, or in comparable liquid solution (shake cultures), maintained at approximately 26 C. Shake cultures enlarge most rapidly, but both maintain similar patterns of anatomical development. Typically, marginal parenchymatous cells of the sac become meristematic and develop, largely by periclinal division, generalized cambial meristems that enlarge the callus by the addition of linear rows of cells. Chloroplasts and wound tracheids with bordered pits mature within 30 days, but to date no further differentiation has been noted. Surface cells frequently enlarge, detach, and grow into branched hyphal aggregations of cells. Media containing 1.0 mg/liter kinetin causes greater enlargement of callus than media with 0.02 mg/liter kinetin.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06101.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

The segregation of a marker characterized by pale green gametophytes was monitored within an inbreeding study of the polyploid fernCeratopteris. Although all of the sporophytes showing segregation were derived from the self‐fertilization of haploid gametophytes, a low overall frequency of 2.5% pale gametophytes was observed in the F3–F5generations. A model based upon a duplicated locus and homoeologous chromosome pairing can explain the segregational behavior within the study. The overall level of homoeologous pairing was determined to be 10%. Occasionally, green gametophytes that were presumably heterozygous for the marker contained pale sectors. This behavior may involve mitotic crossing‐over between homoeologous chromosomes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06102.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

InEchinocereus reichenbachiidichotomous branching and fasciation (cresting) are rare events. Both were found together in only a few of many populations investigated and are interpreted as variants of a single phenomenon. They may occur at any stage of shoot development, but crest meristems arise most commonly on young branches among clusters of normal shoots. Sometimes they appear on unbranched young plants or seedlings, very rarely on older shoots. Dichotomy results from the division of an apical meristem into equal parts each of which functions independently, producing a forked shoot. Fasciation involves the extension of a single meristem into an apical ridge. The product is a flabellate shoot that becomes undulate if growth along the summit continues. In longisection linear meristems appear similar to radial sections of normal shoots; in median sagittal section they have a much extended central mother cell zone within which the cell pattern resembles a rib meristem. Although crest meristems become sluggish or even inactive with age, localized renewed growth may occur spontaneously or be induced by injury. In this species the random production of normal shoots from crest meristems (defasciation) was not observed, but if much or all of such a meristem is removed, branches may arise from lateral areoles, and these are always normal. It seems, therefore, that whatever induces fasciation inE. reichenbachiioriginates in and is restricted to the apical meristem and its immediate vicinity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06103.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Chromosome numbers are presented for 100 collections of Cactaceae from the Trans‐Pecos region of Texas. A total of 65 taxa representing 52 species and 12 genera were counted, including first reports for 45 taxa and new ploidy levels for four taxa. Notable among those listed are counts forOpuntia schottiivar.grahamii(n= 11, ca. 22),O. stanlyi(n= 22),O. arenaria(n= 11),O. phaeacanthavar.spinosibacca(n= 22),O. lindheimerivar.lindheimeri(n= 11),O. strigil(n= 11),Echinocereus enneacanthusvar. cf.dubius(n= ca. 22),E. pectinatusvar.neomexicanus(n= 22), andThelocactus bicolorvar.bicolor(n= 22). Endomitosis was found to be present inO. phaeacanthavar.spinosibacca, Mammillaria pottsii, andNeolloydia intertextavar.dasyacantha. Meiotic irregularities were noted in some species belonging to the generaOpuntiaandEchinocereus. Phytogeographic considerations are inferred from the chromosomal data forO. polyacantha, O. lindheimeri, andO. ficusindica. A base number ofx= 11 in Cactaceae is supported.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06104.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Experiments were performed to determine conditions critical to the isolation and culture of protoplasts from leaf mesophyll cells of aSolanumSectionTuberariumdiploid clone, aS. phureja×S. chacoenseF1hybrid. The optimum concentration of cellulase (Cellulysin) was 0.4%, while pectinase (Macerase) was inhibitory, even at a low concentration (0.075%). Maximum yields of protoplasts were achieved when the enzyme solution was not changed during incubation, and slow oscillation (60 rpm) on a shaker was used. When detached leaves were held under low light intensities or in the darkness for 3–5 days prior to protoplast production, results were more consistent than when the leaves were used directly from the greenhouse. Following dark or low light treatment the optimum osmolarity of the isolation and growth media was approximately 0.3–0.4 M. Of nine growth media tested only those of Nitsch and Ohyama and of Upadhya supported callus development, but the callus was often loose and did not differentiate roots or shoots. Callus from protoplasts cultured in the Upadhya medium modified by addition of glycine, vitamins, and casein hydrolysate, and subsequently transferred to the medium of Lam, formed roots and shoots when cultures were maintained in light. Mature plants were obtained following transfer to modified White's medium and later transplantation to soil.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06105.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Shoot tips ofColophospermum mopane(Kirk ex Benth.) Kirk ex Léonard produce leaves which at maturity are bifoliate and devoid of stipules. Investigation of their early ontogeny, however, shows that these leaves begin as trifoliate structures partially enclosed by their stipules. The latter are fused along their mid regions, forming a tongue‐like “connector.” The lower chamber of this stipule pair harbors the apical meristem while the upper compartment enfolds the two lateral leaflets. The terminal leaflet, histologically resembling the stipules, also fulfills a similar function by covering the top portion of its sister leaflets. Anatomically, the shoot apex displays a pendulum symmetry, with rather steep elevation of that internode portion which subtends the newly formed primordium. Some comparisons with the shoot apex ofHymenaeaare drawn.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06106.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Two acrasid cellular slime molds.Guttulinopsis vulgarisandG. nivea, are compared at the ultrastructural level. The amoebae of the two species are indistinguishable except for the presence of intranuclear fibers inG. vulgaris. Both species share some unusual features, including: plate‐like cristae in the mitochondria, production of microbody‐like organelles in the perinuclear space, spores with thin bilaminar walls, and stalks containing microfilaments bound in striated bundles. These and other observations are discussed with regard to the development of the sorocarps and the relationship of the genus to other members of the Acrasida.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06107.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Pyrrhopappus geiseriandP. carolinianusare partially cross‐compatible (20–52% akene set in artificial crosses). Four barriers to gene exchange prevent or reduce hybridization.Pyrrhopappus geiseriflowers in the early spring, whereasP. carolinianusflowers from mid‐spring to summer with peak flowering in May and June. Overlap in anthesis between the two species is therefore limited. The two species typically occupy different soil‐types,P. geiserion clay soils andP. carolinianuson sands. The diurnal periods of stigmatic receptivity are distinct.Pyrrhopappus geiseriis pollen receptive in the late morning andP. carolinianusat dawn. As a result of the prior three barriersP. geiseriis pollinated by bees of theAndrena verecundacomplex, primarilyA. crawfordi, andP. carolinianusbyHemihalictus lustrans. Pyrrhopappus geiseriandP. carolinianusare almost completely reproductively and ecologically isolated and are not members of one hologamodeme.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06108.x

出版商:Wiley    

年代:1978

数据来源: WILEY