摘要:

At maturity in November, a high percentage ofAster pilosusWilld. seeds germinated in light at high temperatures (30/15, 35/20 and 40/25 C). Stratification during winter lowered the temperature requirement for germination, and high percentages of germination were obtained in light at 15/6 and 20/10 C., as well as at 30/15, 35/20 and 40/25 C. Stratification in darkness was completely ineffective, but stratification in light was partially effective in overcoming the light requirement for germination. Inability of seeds to germinate at low temperatures prevents germination after dispersal in late autumn and winter, when freezing temperatures could kill the seedlings. The lowering of the temperature requirement for germination during winter stratification allows the seeds to germinate and the resulting vegetative rosettes to become well established before the onset of the periodic summer droughts that occur in habitats occupied byA. pilosus.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06185.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

A comparison of a natural, undisturbed ecosystem, a mid‐elevation sage community, with a severely disturbed old roadbed through this community revealed that more than 99% of the plant cover in the natural community was mycorrhizal (vesicular‐arbuscular), whereas less than 1% of the plant cover in the disturbed area (roadbed) was mycorrhizal. Examples of nonmycorrhizal plants as primary successional species in severely disturbed habitats are discussed. The importance of maintaining or re‐establishing the mycorrhizal fungal component in reclamation programs designed to produce stable ecosystems is emphasized.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06186.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

Populations of the endomycorrhizal fungusGlomus fasciculatuswere significantly reduced following land disturbance in western Colorado soil. A bioassay was developed to measure changes in the endomycorrhizal population. In the bioassay, inoculum levels were measured by comparing the percentage infection in corn (Zea mays) root systems thirty days after planting in undisturbed or disturbed soils. The percentage infection was 2% in the disturbed soil compared to 77% in the adjacent undisturbed soil.Glomus fasciculatuswas identified as the endophyte in both soils. Considering the importance and function of endomycorrhizal fungi to their plant hosts the reduction of active inoculum in the disturbed soil may be an important ecological factor in subsequent succession.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06187.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

Small sporangia borne abaxially on pinnules attached toBotryopterisfoliar members are described from coal ball petrifactions of Early Pennsylvanian age. This is the first report of laminar sporangia in this genus. Sporangia are stalked and borne singly near lateral veins onSphenopteris‐like pinnules. Individual sporangia are of the leptosporangiate type, with a lateral annulus and a dehiscence zone of thin‐walled cells immediately adjacent to the annulus. Spores are small, trilete, triangular in outline, typically have blunt spines covering the exine, and correspond to the dispersed spore generaAcanthotriletes, Leiotriletes, orLophotriletes. These sporangia and their spores are unlike previously described globoseBotryopterisfructifications from the Middle and Upper Pennsylvanian, but are similar to sporangia produced by modern members of the Osmundaceae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06188.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

We studied the distributions of flower color, flower morphology, and putative pollinators in eight communities in the western Cascades of Washington and 14 communities in the eastern Cascades. These two forested regions differ in the proportions of species in each flower color and morphological type such that the eastern region is more complex. The putative pollinators of each species were determined from morphological and color properties of the flowers and from the recent, extensive literature. The floristic complement of the western region appears to be serviced by a collection of pollinators that is less diverse than that of the east. In each region there is a strong positive correlation between species richness and flower color diversity, floral morphology diversity, and putative pollinator diversity, respectively. These comparisons suggest the competition for pollinators has led to greater niche differentiation in the eastern regions and that this factor, combined with greater habitat complexity, results in the far greater species richness of the eastern region.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06189.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

3H‐uridine administered as a one‐ or two‐hour pulse to embryogenic pollen grains of freshly excised anthers ofHyoscyamus niger(henbane) was autoradiographically localized in embryoids formed during a subsequent chase. Although continuous incubation of anthers in actinomycin D inhibited embryogenesis, a small percentage of potentially embryogenic pollen escaped inhibition if anthers were grown for at least one hour in the basal medium before actinomycin treatment. The results imply that certain pollen grains become embryogenically determined immediately after culture of the anther and that this is accompanied by the synthesis of ribonucleic acid.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06190.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

Changes occurring within the seed coat ofCuscuta campestrisYunkr. during desiccation were correlated with a decrease in germinability. Germination initially increased as the embryo matured, but then decreased as the testa dried. Completion of macrosclereid development signaled the onset of dormancy. Mechanical scarification with sandpaper or immersion in concentrated H2SO4broke dormancy. The impermeable layer is a region above the light line and at the junction of the hypodermis and the palisade cell layers. This region appeared to be deposited during desiccation of the hypodermis. Overwintering or a period of cold storage also broke dormancy. The change in permeability was found throughout the testa rather than in a specific area.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06191.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

The developmental anatomy of apically stable periclinal chloroplast chimeras was studied in a number of monocotyledonous genera. Their ontogeny is basically similar to that of dicotyledons. In both there are three independent apical layers (L‐I, L‐II, and L‐III) whose derivatives can be traced in stem, leaf and flower. The bulk of the stem tissue is derived from L‐III with only the epidermis and one or two hypodermal cell layers from L‐I and L‐II. All three layers participate in formation of the leaf with great flexibility in the amount of tissue from each. There is more instability in growth of most monocotyledonous leaves than in dicotyledonous leaves. As a result there is relatively more tissue derived from L‐I and L‐II and less from L‐III. The same is true in floral development so that a significant number of gametes are of L‐I origin. As in dicotyledons, there is variation in direction, timing, and frequency of cell division. However, an overriding genetic control results in normal size, shape, and structure. The evidence from genetic and cytochimeras in both monocotyledons and dicotyledons has provided direct experimental proof of the functional reality of the apical layers described by Hanstein and Schmidt.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06192.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

Prolonged apical growth of the leaf primordium and the presence of distinct marginal meristems do not occur inSenecio rowleyanus. Intercalary cell divisions accompanied by radial expansion of derivatives from an adaxial meristem account for the spherical shape of the leaf. The “window” in the lamina marks the position of the adaxial meristem and precludes interpretation of the leaf as being unifacial. Stomata are mesoperigenous and anomocytic in type. Schizogenous secretory canals occur in both the leaf and the stem, and their association with vascular bundles is discussed. The anatomy of the leaf is interpreted in terms of xeromorphy.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06193.x

出版商:Wiley    

年代:1979

数据来源: WILEY

摘要:

Degradation of chloroplasts is shown in mesophyll cells of primary leaves of wheat. The sequence of ultrastructural changes in chloroplasts of naturally senescing leaves is compared with that of detached, aging leaves. In chloroplasts of naturally senescing leaves, the first indications of aging are the appearance of osmiophilic globuli and reorientation of the thylakoidal system. The membranes of the grana and intergrana lamellae then become distended and later dissociate into distinct vesicles. Concurrent with these membrane changes, osmiophilic globuli increase in size and number, and the stroma breaks down. Finally, the chloroplast envelope ruptures and plastid contents disperse throughout the cell's interior. In chloroplasts of mesophyll cells in detached, aging leaves, initial changes also include appearance of osmiophilic globuli, but later stages of chloroplast degradation are different. The chloroplast envelope ruptures before the lamellae break down. Swelling of grana and intergrana lamellae is not pronounced and, additionally, the thylakoidal system degenerates without forming vesicles or numerous osmiophilic globuli. These differences in the sequence of chloroplast degradation indicate that naturally senescing leaves rather than detached, aging leaves should be used in studies of chloroplast senescence.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1979.tb06194.x

出版商:Wiley    

年代:1979

数据来源: WILEY