The Relation of Soil Moisture to Cleistogamy in Stipa leucotricha

Abstract

Plants of S. leucotricha were grown in porous pots and glazed crocks with (1) soil moisture at field capacity, 33% of dry wt. or periodically drying down from field capacity to (2) 23% of dry wt., or (3) 13.5% of dry wt. (wilting %), or (4) 8% of dry wt. (nearly air dry). Plants under treatment (1) produced about 10% cleistogamous florets, under (2) 46%,under (3) 57%, and under (4) 94%. This correlation between soil dryness and cleistogamy was best shown by plants in pots where soil dried out faster than in crocks. The differences in morphology, time of maturity of parts, time of pollination and seed set between cleistogamous and chasmo-gamous florets are discussed. Apparently this environmental factor is able to modify the genetic expression of the plant and is explainable on a threshold basis.