The germination response to 16 alternating temperature regimes in the 4 to 25% range of 6 grasses and 3 legumes adapted to semi-arid range, with wheat and barley for comparison, was consistent with that to fixed temperatures. No stimulating effect of alternating temperatures was noted. The retarding effect of adverse temperatures was stronger than would follow from their relative influence on weighted mean temperature, and germination does not seem to respond to hour-degrees. The data support conclusions reached in earlier work concerning the critical role of low temperature in semi-arid range seeding failures.