Some Hydration Reactions and Growth. 



149 



ing while in a shrinking stage. These differences hold for the morning, 

 except that the effects of acid and hydroxid are about equal. 



TABLE 110. 



An additional set of measurements with young leaves decreased the 

 differential between the more acid condition of the morning and the 

 less acid condition of the evening, as is shown in table 111. 



TABLE 111. 



Young leaves are generally in a state of enlargement both morning 

 and evening, and should show but little difference in swelling capacity 

 in the two stages, while mature leaves are enlarging in the morning 

 and shrinking in the afternoon, in expression of a condition which is 

 reflected in the swelling reactions. Thus, for example, sections of 

 mature leaves taken in the morning, which had a thickness of about 

 9.3 mm., swelled 6 per cent at 14 to 19 C. in the dark room, which was 

 about the temperature at which they were taken. An equivalent set 

 taken at 1 p. m. swelled 15 per cent in water at 17 to 19 C. From 

 which it may be seen that the measurements of variations in thickness 

 of entire leaves (see pp. 147, 148) are in entire conformity with other 

 known facts. 



The foregoing measurements were obtained from segments cut 

 from leaves about 1 cm. in length and with the epidermis on the three 

 faces intact. The measurements made for the purpose of determining 

 the possible effects of acidity were obtained by cutting slices which 

 removed one angle of the leaf and the epidermal face parallel to the 

 excised surface. If the water-loss is a factor, its effects would be most 



