1. Germination studies carried on in soil in pans, and in a seed germinator, indicated wide average differences among plants of Poa pratensis in the number of seeds set and also in the viability of such seeds. Although germination percentages of a few plants were less than 10%, most plants produced seed of good viability. The poor seed set of some plants was due to frequent collapse of the developing macrosporocyte during or just after meiosis. Significant differences in the amount of such sterility was determined for between-progeny comparisons. Plants within a given progeny were significantly different among members in one progeny, that is, 72. 2. Forty-four progenies from as many plants of four related parental families were grown. The frequencies of aberrant plants among the second-generation individuals varied from zero to 100%. There did not appear to be any direct relation between the morphological characteristics of parent plants and the breeding behavior of their progenies. This also appears true...