STOMATA AND HYDROLOGIC CYCLE

Shrinking stomata in the needles of 16 m pine trees by a single spray of 300 ppm phenylmercuric acetate on June 2 decreased the contraction of the tree boles that is caused by dehydration during rapid transpiration. It did not stunt the needles but did decrease growth of the bole 15%. The decrease in evaporation caused by stomatal shrinking was sufficient to cause a 20 to 28 mm smaller depletion of soil moisture between June and Oct. Since this significant change was but 5% change in evaporation and since stomata were affected only part of the season, these microscopic pores may provide a strategic means for changes of great scope in the hydrologic cycle.