摘要:

Pollen-cone and seed-cone buds which differentiated in the summer and fall of the year before pollination resumed development in early April after about 5 months of dormancy. The sporogenous cells present in the dormant pollen-cone bud divided and formed pollen mother cells which began meiosis by mid-April. Meiosis was completed by late April and mature five-celled pollen was formed by the 3rd week of May. Wind pollination occurred in late May.Each ovule developed a curved funnel-shaped integument tip with a shallowly notched flange-like lip to which pollen readily adhered. No pollination drop was observed. Pollen remained attached to the integument tip but did not germinate for about 1 month, during which time the nucellus grew out nearly to the micropyle and the lip of the integument folded slightly inward bringing the pollen close to the nucellar tip. Pollen tubes then developed rapidly and penetrated the nucellus during the 1st week of July.Each ovule contained a single large megaspore mother cell in the dormant seed-cone bud. Megaspore mother cells underwent meiosis in early May and the single functional megaspore began free nuclear division in mid-May. Female gametophyte development was similar to other members of the Pinaceae and was completed by the end of June. Archegonia varied from two to three and each had two tiers of neck cells.Fertilization occurred in mid-July and early embryo development was rapid. Both simple and cleavage polyembryony occurred and 16-celled proembryos formed. By late July, usually only one club-shaped embryo remained in each ovule. Distinct meristems and cotyledons developed in the embryos in early August and embryos were mature by late August. Ovuliferous scales, usually with two seeds attached, began to be shed in late September. All ovuliferous scales were shed by November.Poor seed production inAbies amabilis(Dougl.) Forbes results partly from the low cone-bearing capacity of the trees, the infrequent occurrence of abundant pollen and seed cones at the high elevation sites, and the high incidence of insect damage to seeds and cones. In addition,A. amabilisand other species ofAbieshave an unspecialized pollination mechanism, a long period of pollen dormancy after pollination, and a very short time after germination when pollen tubes must develop and penetrate the long nucellar tip. InA. amabilisthe archegonia abort very quickly if they are not fertilized. This period when fertilization can effectively occur is very short and remarkably synchronized within a cone and a tree. These, plus the low number of archegonia, may be reasons for the low percentage of viable seed inA. amabilis.

ISSN:0008-4026    

DOI:10.1139/b77-303

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Thirty reciprocal crosses among three sympatric species ofVaccinium§Cyanococcusfrom Highlands County, Florida, show a significant difference in seedling success among the heteroploidsV. darrowii(2n = 24) andV. myrsinites(2n = 48) as well asV. fuscatum(2n = 24) andV. myrsinites, but no significant difference in seedling success was observed in crosses between the homoploid taxaV. darrowiiandV. fuscatum. The small number of naturally occurring hybrids of these homoploid taxa can be explained by weak incompatibility barriers within the style which result in a consistently longer time for both seed maturation (12% longer) and seed germination (11% longer) in the interspecific cross.

ISSN:0008-4026    

DOI:10.1139/b77-304

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A study of environmental effects on lateral bud growth in the sunflower,Helianthus annuus, showed that the provision of a high relative humidity (90 ± 5%) in conjunction with a high light intensity (about 30 000 lx) and an abundant N supply (420 ppm) permitted the buds at the basal nodes to escape from apical dominance and to develop as lateral branches. A reduction in any one of these three factors was sufficient to prevent the release of the buds from inhibition. The marked effect of humidity on bud growth suggested that the degree of water stress is the factor most likely to limit the growth of the lateral buds under field conditions. The mode of action of water stress and the N supply is discussed in relation to the genetic control of bud activity and to the role of nutrient competition in the mechanism of apical dominance.

ISSN:0008-4026    

DOI:10.1139/b77-305

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The effects of short-term exposures to polychlorinated biphenyls were investigated usingChlorella vulgarisand isolated spinach chloroplasts as experimental material. WhenChlorellawere immersed in a Warburg-Buck medium to which 10 mMglucose had been added. Aroclor 1221 was found to cause a significant inhibition of the respiration rate at concentrations above 10−7 M. WhenChlorellawere immersed in the same Warburg-Buck medium to which no glucose had been added, Aroclor 1221 caused a stimulation of the respiration rate at concentrations above 10−5 M. There appeared to be little effect on photosynthesis inChlorellawhen Aroclor 1221 was present even at concentrations as high as 10−3 M. In contrast, oxygen evolution from isolated spinach chloroplasts using potassium ferricyanide as the electron acceptor was inhibited by Aroclor 1221. This inhibition was also apparent when the uncoupler ammonium chloride was present. Since there was no inhibition when photosystem I was examined on its own, it is suggested that Aroclor 1221 can inhibit photosynthesis in spinach chloroplasts at a site on the electron transport chain close to photosystem II.

ISSN:0008-4026    

DOI:10.1139/b77-306

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Phillipsia rugosporaandP. guatemalensisare described as new species from Costa Rica and Guatemala, Central America.Phillipsia rugosporais distinguished by its yellow hymenium and wrinkled (under the SEM) ascospores.Phillipsia guatemalensishas a rosaceous tan hymenium, relatively thin flesh, and striate ascospores. Both species have been grown in culture.Phillipsia guatemalensisproduces holoblastic, hyaline conidia on a low-nitrogen medium.Phillipsia rugosporadoes not form conidia in culture. However, small, conidium-like structures are produced by germinating ascospores of the latter species.

ISSN:0008-4026    

DOI:10.1139/b77-307

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Specimens ofRadiigera fuscoglebaZeller andGeastrum limbatumFries were studied bothin situand microscopically during their development and are described in detail. They were found to contain identical cell and tissue types, differing only in the manner of dehiscence of the fruiting body at maturity. The same tissue types were observed in five additional species, four inGeastrumand one inRadiigera. The genusRadiigerais transferred to the Geastraceae. New distributional records for the two species ofRadiigeraand forGeastrum limbatumare reported for the Pacific Northwest along with photographs and illustrations of the microscopic features of both taxa.

ISSN:0008-4026    

DOI:10.1139/b77-308

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A survey of four old grasslands near London, Ontario, showed that different legumes formed consistent relationships with different grass species. Each legume was strongly associated with a particular combination of grass species. It is suggested that each legume–grass combination is selected through the ability of the combination to utilize the soil environment more efficiently than random combinations of species. The ability of species to combine as well as compete is an important factor in maintaining the dynamic stability of grasslands.

ISSN:0008-4026    

DOI:10.1139/b77-309

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Light microscopic and scanning and transmission electron microscopic observations were obtained on azygosporogenesis inMucor azygosporusBenjamin. Terminal gametangia are delimited by centripetally growing septa but plasmodesmata maintain cytoplasmic continuity between the azygophores and gametangia. Warts develop as regularly spaced patches of electron-opaque wall material on, and ultimately within, the inner primary wall. The mature complex azygosporangium wall is composed of (1) remnants of the membranous outer primary wall, (2) the ornamented layer of electron-opaque, stellate, confluent warts, and (3) a fibrillar, electron-opaque, tertiary layer. A homogeneous, hyaline azygospore wall (quaternary layer or endospore) with stellate warts is laid down within the azygosporangium. A comparison of the fine structural aspects of zygosporogenesis and azygosporogenesis in the Mucorales is presented.

ISSN:0008-4026    

DOI:10.1139/b77-310

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Morphogenesis of azygospores induced inGilbertella persicaria(+) by the illegitimate cross of this species withRhizopus stolonifer(−) was examined by light microscopy and transmission and scanning electron microscopy. Gametangia were formed only inG. persicaria. A continuous secondary azygospore wall was laid down within the original gametangial walls, and it was within this secondary wall that the conical, electron-opaque warts developed. Simultaneously, autophagic vacuoles filled the suspensor ofR. stolonifer. Mature azygosporangia possessed a black outer ornamental layer consisting of connate truncate, conical warts. Azygosporangia were adjoined by intact fusion septa at their interface with aR. stoloniferprogametangium. The significance of azygosporangia induced during imperfect hybridization was discussed in relation to the taxonomy and biology of the Mucorales.

ISSN:0008-4026    

DOI:10.1139/b77-311

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Vegetative buds ofPicea glauca(Moench) Voss were studied throughout the annual growth cycle in several trees in 1975 and 1976 and bud development was related to lateral vegetative shoot growth, date, and temperature sums.Vegetative buds became mitotically active in mid-April at lower elevations and about 6 weeks later at higher elevations. Shoot elongation was characterized by similar smooth sigmoid curves in both years. Shoot growth was slow for the 1st month, rapid during the 2nd month, and slow again for the 3rd month and ended by early August. Temperature sums related best to percentage of shoot elongation if the end of vegetative bud dormancy was used as the starting date and 5 °C was used as the threshold temperature. Arbitrarily chosen starting dates and threshold temperatures gave temperature sums which were related to shoot elongation only when shoot elongation was nearly completed. Generally, if the end of vegetative bud dormancy is known, the number of days from that time is nearly as accurate as the more complex use of temperature sums in predicting the percentage of shoot elongation or the stage of vegetative bud development.Bud-scale initiation occurred during shoot elongation. Axillary buds were initiated in mid-May and flushing occurred when shoots had elongated to about 30% of their final length in late May or early June. The end of shoot elongation coincided with the onset of leaf initiation on all trees in both years. The change from bud-scale initiation to leaf initiation was preceded by a marked increase in apical width and a slight increase in apical height and mitotic frequency. Leaf initiation was rapid for 6 weeks then slower for the last 4 weeks. Vegetative buds became dormant in mid-October.Vegetative bud development is closely related to shoot elongation. Breaking of vegetative bud dormancy was not affected by temperature but shoot elongation and flushing were affected by temperatures which occurred after dormancy was broken.

ISSN:0008-4026    

DOI:10.1139/b77-312

出版商:NRC Research Press    

年代:1977

数据来源: NRC