摘要:

Histochemical determinations for storage of carbohydrates in rhizomes, roots, and young shoots ofTypha latifoliaL. (Typhaceae) were conducted during the overwintering period from November to April. Early winter analysis showed that rhizomes and roots contained large amounts of starch (45.03% and 22.80% dry weight, respectively). The major storage tissue was parenchyma of the rhizome central core. From winter into spring a gradual decrease in storage starch in the rhizome and root occurred concurrently with starch accumulation near zones of rapid development in young shoots (buds), but the rhizome retained much starch (27.40% dry weight) into the start of its 2nd yr.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb07803.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Roots ofMarsilea vestitaranging from 1–120 mm in length, as well as root primordia, were analyzed to determine mitotic activity and ploidy levels in the apical cell, five well‐defined regions of the root proper, and two regions in the root cap. The mitotic index of the apical cell tended to be above the overall mean mitotic index for the entire apical meristem. No diurnal rhythm in mitotic index was apparent. The cell‐cycle duration of the apical cell ranged from 12.1–25.2 hr, that of other regions of the root from 16.1–41.5 hr. There was no indication of polyploidy in any part of the apical meristem except in a few procambial cells. Thus, the results support the classical concept that the apical cell is the ultimate source of cells in the root.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb07804.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

The course of the vascular system in the proximal end ofDolerotheca formosais described. Vascular bundles flare outward and downward immediately upon entering from the peduncle. These bundles are located in radiating septa just beneath the cover and give off small lateral bundles pinnately. Laterals from adjacent septal bundles meet, fuse, and extend downward in the parenchyma plate separating paired sporangia. The septal bundles, therefore, alternate in position with the parenchyma plate bundles and are interpreted as remnants of an ancestral bifurcating pinna system, which bore pendent sporangia along each side of supporting rachises. This interpretation differs from both theCodonothecaaggregation and plicatedWhittleseyahypotheses recently advanced to explain the evolutionary pathway by which this complex pteridosperm pollen organ evolved.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb07805.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Fatty acid analyses of seed lipids in 46 species ofCupheaare presented, representing the first major survey of a molecular nature for the family. A remarkable diversity in composition is found, with seeds containing high amounts of several medium chain fatty acids. Lauric acid (12:0) predominates in 43% of the species studied, constituting 50–74% of the total fatty acid content. Capric acid (10:0) is the dominant fatty acid in 32% of the species, comprising as much as 87% of the total acid content. Caprylic acid (8:0) predominates in one section of the genus. The emphasis on production of fatty acids with carbon chain lengths of 12, ten, and eight carbon atoms is unique among plant genera studied to date. Among seven of the nine sections studied, one pattern of fatty acid composition predominates. Two sections have no characteristic pattern, supporting other evidence of their polyphyletic origin. The most significant systematic contribution is made by comparison of the predominate fatty acid components in the seed lipids. When used in conjunction with floral morphology, pollen studies, and chromosome number, it provides an important new basis on which to draw inferences of evolution and clarify present relationships within the genus. Additionally, a trend from the longer‐chained, unsaturated linoleic acid (18:2) as a major lipid component to shorter‐chained saturated capric and caprylic acids is correlated with increasing floral specialization. It is suggested that mutations in regulatory genes have occurred which cause fatty acid production in seeds to cease at progressively earlier stages, resulting in accumulation of large amounts of single fatty acids of progressively shorter carbon chain lengths.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb07806.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Thermal discharges from nuclear production reactors killed large areas of baldcypress‐water tupelo (Taxodium distichum‐Nyssa aquatica) forests along streams on the Savannah River Plant in South Carolina. Recolonization by baldcypress has been slow in areas where present stream temperatures do not exceed ambient by more than 10 C and has not occurred at all at higher temperatures. Since it has been previously shown that cypress germination and establishment are not inhibited at stream temperature below 42 C, the growth of 1‐yr‐old baldcypress seedlings introduced into ambient (Tmax= 32 C) and ambient + 10 C (Tmax= 42 C) stream temperatures was examined during a 16‐month period to determine the response of this growth stage. Growth in height, diameter and biomass of these seedlings was enhanced in a stream habitat with maximum water temperatures of 42 C. Allocation of dry weight into root and shoot tissues was modified by stream temperature, with a lower root/shoot ratio in plants at the 42 C location. In thermally altered (‐42 C) areas, neither establishment nor growth of established cypress seedlings is limited by stream temperature. Thus, slow reinvasion of these sites by baldcypress is thought to be due to a lack of a seed source and/or competitive exclusion.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb07807.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Flowers from the Middle Eocene Claiborne Formation of western Tennessee have both floral and palynological features suggestive of affinities with the subfamily Celtidoideae of the Ul‐maceae. Floral size, pollen size, and exine structure suggest that these flowers are intermediate between insect‐pollinated ancestors and the modern wind‐pollinated Celtidoideae. Thus, they represent the first direct fossil evidence supporting the widespread notion that at least some of the Amentiferae have been derived from insect‐pollinated ancestors.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb07808.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

There has recently been concern that some anthropogenic atmospheric pollutants, such as chlorofluoromethanes, may result in a global reduction in stratospheric ozone. This would undoubtedly increase the level of ultraviolet radiation reaching the surface of the earth. Such an increase in solar ultraviolet irradiation might have important biological consequences.Unifoliate leaves of decapitated soybean plants were exposed to 0, 20, 50, and 90 effective mW m2UV‐BBE(weighted ultraviolet‐B irradiance) from special lamps in a greenhouse. The effects of UV‐B radiation were examined in leaves at three different ontogenetic stages: bud; one‐third expanded, and fully expanded leaves. Leaf area expansion, net photosynthesis, specific leaf weight, chlorophyll concentrations, and acidified methanol extract absorbance were measured during the course of the study. These data revealed several generalizations concerning the relationship between leaf ontogeny and photosynthetic response to UV‐B radiation: 1) The rate and duration of leaf expansion are affected by low levels of UV‐B irradiation. 2) There appears to be a shift in the ontogenetic sequence of photosynthetic capacity as a function of leaf age. 3) This results in leaves of similar chronological ages being in different physiological stages of maturity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb07809.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Variability in annual growth increment inPinus ponderosawas measured and heterozygosity level estimated in order to examine the relationship between genetic heterozygosity and phenotypic homeostasis in natural populations of a long‐lived perennial plant. Pollen was collected from 190 ponderosa pine trees in the upper montane region of the Front Range in Colorado and four isozyme systems were resolved electrophoretically from these samples. Each tree was cored, aged, and each annual ring width measured. Statistics estimating within‐tree variation in growth increment were then related to heterozygosity levels. The results indicated a significant positive association between level of heterozygosity and growth variability. Two speculations are offered to account for this relationship.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb07810.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Unrestricted gene flow would be expected to lead to similar chromosome knob frequencies in sympatric populations of maize and teosinte. Chi‐square tests were therefore used to compare chromosome knob frequencies of 45 collections of Mexican teosinte, grouped according to six geographic regions, with sympatric and allopatric populations of maize. Comparisons of knob frequencies between sympatric and allopatric populations within each region produced an initial classification for each knob‐forming position. Further comparisons for each knob position over all regions, led to an interpretation of results for sympatric populations of maize and teosinte in terms of gene flow, selection, differentiation, ancestral similarities, and ancestral differences. Within regions, a high number of knob positions suggesting gene flow was associated with a low number of knob positions suggesting recent differentiation, and vice versa. It is suggested that the teosinte populations most likely to represent unique sources of germplasm are those most susceptible to future genetic erosion by maize. These relationships may represent a general model applicable to a number of crop plants and associated weed races.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb07811.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Increase in cell number, and in anlage volume and length have been investigated during the development of lateral root primordia in roots of intact plants ofPisum sativumandVicia fabaand in excised roots of both species cultured in White's medium supplemented with 2% sucrose. With the exception of primordia in excised roots ofVicia, the general equation which best described increase in each aspect of primoridium growth measured against time was that for exponential growth. When the times necessary for cell number and primordium volume and length to double were determined at intervals over the period of development studied, however, they were found to vary. Similarly, estimates of the size of the proliferative fraction of cells at different times during anlage development indicated that this index of meristematic activity also fluctuated over the developmental period investigated, i.e., increase in cell number and in primordium volume and length do not occur in a truly exponential fashion as the primordia increase in size and cell number.One difference between anlage development in the roots of intact plants and in those grown in culture was that whereas the former primordia completed their development and emerged as lateral roots over the period of the investigation, the latter did not. Moreover, cell doubling time and anlage volume and length doubling times were longer, and the proliferation fraction of cells lower, over the whole period of, and at intervals during, primordium development in the excised roots compared with the results obtained for the roots of the corresponding intact plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb07812.x

出版商:Wiley    

年代:1981

数据来源: WILEY