juneio. i9i8 Transpivation of Com and the SorghuTYis 581 



to their position in the open amounted to five or six minutes. The loss 

 of water from the plants was determined in most of the experiments every 

 two hours from 7 a. m. to 7 p. m. Determinations were made in two 

 experiments in 191 6 for each 2-hour period of the night, but since the 

 loss of water from the plants during the night was very small, it was not 

 deemed of sufficient importance to carry the night experiments further. 

 After an experiment had been completed the leaves and sheaths of the 

 plants were cut in convenient lengths and the outline of these portions 

 carefully traced on unruled paper with a hard lead pencil. The areas 

 inclosed by these outlines were then determined by means of a polar 

 planimeter. From the areas thus obtained the rate of transpiration per 

 unit of leaf surface was calculated. 



EXPERIMENTAL DATA 



Five experiments were conducted in 191 6 and eight in 191 7. In the 

 former year three varieties of plants were used in each experiment, while 

 in 1 91 7 four varieties were used. With the exception of two experi- 

 ments in 1 91 6, the transpiration was determined every two hours from 

 7 a. m. to 7 p. m. and for a period of two or three days. The results of 

 the different experiments are shown in Tables II and III. The loss of 

 water is expressed in grams per plant per hour, while the rate of transpi- 

 ration is expressed in grams per square meter of leaf surface per hour and 

 in grams per square meter of combined leaf and sheath surface per hour. 

 The average hourly evaporation for each 2-hour period is also recorded. 

 The data shown in these tables are expressed graphically in figures i to 13. 

 In these figures the relative leaf surface of the plants used in each experi- 

 ment is also shown. A general description of the plants used in each 

 experiment is given in Table 1. 



