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Increases in the Diffusion Resistances of Leaves in a Carbon Dioxide-Enriched Atmosphere 总被引:1,自引:0,他引:1
The stomatal closing reaction to CO2, which has been observedin laboratory studies by many workers, was investigated in plant-growthcabinets under conditions similar to those in glass-houses withCO2-enriched atmospheres. Lettuce and Xanthium plants grownin a normal atmosphere showed the expected stomatal closurein response to increasing CO2 concentrations, and lettuce plantsgrown in 1000 ppm CO2 showed the same response, even after 4weeks. Thus there was no evidence of acclimatization of thestomata and it is concluded that they must remain partiallyclosed during CO2-enrichment. Estimates of diffusion resistancesto CO2 intake in lettuce leaves showed that in light of 14.4J m2 S1, 880 ppm CO2 in the atmosphere resultedin a concentration of 367 ppm near the mesophyll cell walls.If the stomata remained open this same internal concentrationcould be achieved with an external concentration of only 640ppm. There could, therefore, be some economic advantage if stomatalclosure were prevented during CO2-enrichment. 相似文献
173.
Comparison by soil-block tests on several timbers of the wood-destroyingabilities of dicaryotic cultures of both Poria vaillantii andLenzites trabea with those of monocaryotic cultures either derivedfrom, or contributing to, the formation of the dicaryon, indicatedthat monocaryotic cultures of P. vaillantii were generally moredestructive than related dicaryotic cultures, whereas dicaryonsof L. trabea tended to be slightly more destructive than relatedmonocaryons. The tolerance of L. trabea monocaryons to coppersulphate and to sodium arsenate in nutrient agar showed someindication of being higher than that of related dicaryons, whilstthe tolerance of P. vaillantii monocaryons to a copperchrome-arsenatepreservative in soil-block tests also appeared to be higherthan that of related dicaryons. It is concluded that, althoughneither wood-destroying ability nor preservative tolerance wasgreatly affected by nuclear condition, the differences shownmay be of importance in conjunction with the monocaryotizationof dicaryons by toxic agents during laboratory decay tests. 相似文献
174.
Use of a model and toxicity data to predict the risks to some wild plant species from drift of four herbicides 总被引:2,自引:0,他引:2
The dose responses of 14 wild plant species (two grasses, two legumes, one annual and nine perennial dicotyledons), not usually recognised as weeds, to four herbicides (asulam, glyphosate, MCPA and mecoprop) were measured in glasshouse experiments. Glyphosate was the most toxic; seven of the species tested had EDu, values (measured as shoot dry weight) of < 1.0 μg/plant, compared with only one species for MCPA and mecoprop. Asulam was the least toxic. Results were used to indicate the risk to each species from drift damage. A model of spray drift, based on that developed by Thompson & Ley (1982) for evaporating droplets, was rescaled to allow for field application rates and used to predict the distances travelled by given doses of herbicide. This gave acceptable agreement with reports for drift damage in the field, and predicted that only glyphosate sprayed at the highest recommended concentration might be unsafe to some of the species examined. The two herbicides sometimes used as volatile formulations (MCPA and mecoprop) did not cause damage at the small doses likely to result from exposure to vapour in the field. 相似文献
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ELIZABETH LEWIS CARET MUNGER RUTH WATSON DONALD WISE 《The Journal of eukaryotic microbiology》1974,21(5):647-649
SYNOPSIS. Polytomella caeca (Phytomonadida, Polyblepharidae) reproduce by binary fission and sexual reproduction. The sexual process increases in frequency as the population becomes denser. Normally 2 monoecious isogametes engage their anterior flagella prior to fusion, which occurs by merging of the cells from their anterior to their posterior ends. This is followed by a period of zygotic enlargement before cleavage of the zygote into 4 daughter cells. Encystment occurs throughout the flagellates' bloom until they represent 80% of the individuals at the end of the bloom. Cysts are a resistant, not reproductive stage. The observations were made over long periods of time by following individual flagellates in microcultures and by viewing living cells taken at various stages from larger cultures. 相似文献