Ecology of Desert Plants. II. The Effect of Rain and Temperature on Germination and Growth

In the previous article (Went, '48) observations were reported, showing that the difference in summer and winter vegetation of annual plants in desert areas is due to differential germination, and is not caused by competition, or by differential dying of seedlings or older plants. To supplement these field observations and to test the validity of the conclusions reached, experiments were carried out in the air-conditioned greenhouses at the California Institute of Technology (Went, '43). The experiments on germination of individual seed lots will be reported later, giving a purely physiological analysis of each species. Some work of this kind on other plants has been reported earlier (Lewis and Went, '45). The present paper deals with top soil carrying its normal content of seeds; when such soil is brought under controlled conditions, it is possible to determine to what extent the density of vegetation and floristic composition of a given area are limited by (1) the seed present, (2) the germination conditions, and (3) the climatic conditions that are influential in seedling survival and later growth.