A stepwise multiple regression analysis was used in an attempt to correlate statistically the geographic patterns in the abundance of C grasses with patterns in climatic variables. The percent of grasses having the C pathway was computed for the total grass flora in twenty-seven widely spaced regions of North America. From long-term climatic records seasonal and annual values for solar irradiance, water supply, heat availability, and combinations of these variables were assigned to each of the twentyseven regions. The results of the analysis suggest that high minimum temperatures during the growing season have the strongest correlation with the relative abundance of C grass species in a regional flora. It appears that the deleterious effects of low temperatures during growth negate the advantages of possessing the C pathway in cooler habitats.

No abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Ecology. SUMMARY(1) A whole-community investigation of allelopathy in an old-field in Illinois was undertaken, by comparing bioassay results with association patterns in the field.(2) The seven most abundant species in the field were tested upon each other in nine commonly-used bioassays. Eight of the nine bioassays gave many cases of statistically significant inhibition, and strong phytotoxicity was exhibited by species which have not previously been suspected of being allelopathic and which show no readily-observable signs of allelopathy in the field.(3) Autotoxicity was found to be as severe as allotoxicity, indicating that the species have not evolved resistance to their own inhibitors.(4) When the distribution patterns of species in the field were statistically compared with the results of each of the bioassays in turn, no significant correlations were found.(5) It was concluded that the types of allelopathy which were tested by these bioassays were not demonstrably effective under field conditions, that perhaps any species can be shown to have allelopathic properties in bioassays, and that bioassays may, for many communities, have no ecological meaning.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.

The interaction between the phytotoxicity of certain phenolic compounds and deprivation of certain nutrients was investigated by means of a factorial experiment. Two concentrations of p-coumaric acid and two of vanillic acid were added to nutrient solutions containing various quantities of nitrogen and phosphorus, and these solutions were tested on barley plants in sand culture. Phenolic toxicity appears to depend intimately on nutrient concentrations; the phenolic acids were uniformly and significantly inhibitory only at low nutrient concentrations. Allelopathy with phenolics as chemical inhibitors seems most likely to occur in nutrient-poor soils.