Some Aspects of the Autecology and population Biology of Phacelia purshii

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Abstract
P. purshii Buckl. is a winter annual; germination occurs in autumn and mature seeds are dispersed in late May and June. Seeds are dormant at maturity and afterripen during summer. Optimum temperature for germination of afterripened seeds is 30/15.degree. C, and seeds germinate better in light (14 h photoperiod) than in darkness. During annual population establishment in autumn, seed germination rate greatly exceeds seedling death rate, but nevertheless, many seedlings die during this period. In 1971, 36.8% of the plants germinating in eight .04 m2 quadrats died during autumn, and only 29.3% survived to reproductive maturity. Seed production in the same plots ranged from 997-6100 in the spring of 1972. Not all the viable seeds at the population site germinate in a given year, and thus viable, ungerminated seeds are always present in the soil.

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