A STUDY OF WATER RELATIONS OF EPICHLOE-AMARILLANS WHITE, AN ENDOPHYTEOF THE GRASS AGROSTIS-HIEMALIS (WALT) BSP

In this study we measured water losses from various excised parts of p lants of Agrostis hiemalis and stromata of the endosymbiont fungus Epi chloe amarillans. Measurements were made by excising culms from plants , then inserting cut ends into microsedimentation tubes containing wat er and measuring water consumed under defined conditions. It was found that water was lost from the stroma at a rate 10 times faster than th at from the surface of the emergent leaf blade. Comparative studies of stroma-bearing culms with those free of stromata showed that overall water losses in stroma-bearing culms were only slightly higher than wa ter losses in culms without stromata. However, it was found that strom a-bearing culms were significantly reduced in mass when compared to cu lms free of stromata. This mass reduction is suggested to have a compe nsatory effect on water losses. It is suggested that the enhanced rate and unregulatability of the evaporation of water from stromata may ha ve been a key factor in selecting for endophytes that do not produce s tromata.