Effect of Different Water Pretreatments on Potential Transpiration.

The effect of restricted xvater supply or drought periods on transpiration after rewatering the plants has been investigated repeatedly (3, 4, 5, 9, 11, 16). It has been found that, after a periodl of recovery, changes in the transpiration rate in plants grown under restricted water supply relative to those in plants not subjected to water stress may occur. The recorded rates, however, vary widely, and besides consi(lerable increases (3, 5, 16, 17) in the potential transpiration rate, e.g. the rate of tranlspirationi under optimiial water supply, in other investigations only smiiall (4, 12) or no increases (9) have been found. These findings, howvever, are not quantitatively comparable since both the level an(d the dluration of vater treatment, as well as the nmethod of dletermlining transpiration rate, (liffere(l considerably. Furthermlore, in miiost of the investigations only 2 general treatmlenits, wet and dry, were use(l. Evidently, none of these experiments allows ani estinmatioln of the influence of different degrees of (Irought on the potential transpiration rate. Furtlher information mliglht be expected from experimlenits wvith plants growxn under a range of different water treatmilenits, tlhus showving wvhether there exists a specific response of the potential transpirationi rate to various (legrees of drouglht. Since it was also of interest to examine the relation bet\xveen leaf structure and(l tralnspirationi rate. measuremiienits wvere made of number of stomiiata per Unlit area and of leaf surface develop)ment.