Tropism as a Basis for Tolerance of Strawberry Clover to Flooding Conditions 1

FIELD observations indicate that strawberry clover (Trijolium fragiferum L.) is remarkably tolerant to flooding. The physiological basis for this tolerance has received little attention and data are lacking on comparative production under controlled soil-moisture conditions. Survival under prolonged flooding seems to be associated generally with the ability of plants to develop adventitious root systems and porous tissues which serve to improve the ventilating system of the plants. Therefore, it appears that the primary explanation for tolerance to flooding is the differential ability of plants to adapt to unfavorable conditions. Differential adaptive capacity did not appear initially to explain the observed responses of Ladino clover (T. rep ens var. latum L.) and strawberry clover to flooding. These species are similar in growth form, stolon development, and rooting, but Ladino clover is killed under flooding conditions which are not too unfavorable for strawberry clover. The current investigations were undertaken to obtain quantitative data on growth responses of these two species to flooding and to determine the nature of their differential tolerance. These studies ultimately led to the observation that differences in tropic responses occurred which favoredstrawberry clover over Ladino clover. It seemed necessary to determine: firstly, the nature of the tropic behavior of strawberry clover; and secondly,