In an attemDt to studv the nature of plant tolerance to soil acidity and related factors,'a series of investigations was conducted with sand cultures to determine the chemical composition of alfalfa as related to its response to various concentrations of manganese, aluminium and calcium' All clones studied were affected, but to a variable degree, by an excess of manganese and aluminium, They absorbed approximately the same amounts of these elements but considerable differences rvere noted in their rate of translocation from the roots to the aerial orsans. As a result, plants *'hich were the least affeeted hv manqanese and aluminium conrained smaller amounts of those trvo eleme-nts iniheir stems and leaves and larger amounts in their roots.Moreover, for a given content of manganese and aluminium in aerial organsi the degree of irrj-ury was approximatcl-y the same lor all clones. More tolal and witer-solubie ialcium'ii'as found in so-called tolerant than non-tolerant olants. Also. an increase in the calcium concentration of the nutrient culture uas effective'in reducine manqanese toxicity. These results suggest the theory that the rate of u"ptal

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Two groups of alfalfa varieties and crosses were grown in nutrient solutions containing two levels of manganese: 0.5 and 25 parts per million. Significant differences between varieties in their ability to tolerate manganese toxicity were observed. Promising individuals from the variety trial were selected for strain building. Some resulting crosses were found to be highly tolerant to the toxic level of manganese. This character appears to be inherited.

Certain aspects in the quantitative genetics of autotetraploid populations have been developed into a deterministic model. The use of two mating systems, inbreeding and hybridization, on the fertility of two alfalfa clones gave results which were in close agreement with the proposed model. The interactions between more than two alleles, whether identical or not, were important in the expression of heterosis. Performance of hybrids became weaker and weaker as the parents were more and more inbred. It was possible to evaluate the influence of the various genotypic structures on seed setting.

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