6o4 Journal of Agricultural Research voi. xm, no. h 



corn, Blackhull kafir, and Red Amber sorgo, while the number of plants 

 of Dwarf milo, feterita, Dwarf Blackhull kafir, and Freed's sorgo varied 

 from one to three to each can. 



The transpiration was determined in most of the experiments every 

 two hours from 7 a. m. to 7 p. m. Bach experiment extended through 

 two or three days. The cans were weighed on scales of the platform type 

 with a carrying capacity of 180 kilos and were sensitive to about 5 gra. 

 In 1 91 6 the cans were placed in the open on the surface of the ground, 

 but in 1 91 7 they were placed in a pit in the center of a plot that was 

 planted to corn. The pit was of such depth that the tops of the cans 

 were on a level with the surface of the ground. 



The amount of water transpired per plant in a given period stood, with 

 the exception of Dwarf Blackhull kafir in 191 7, in the same relative order 

 as the extent of leaf surface. The amount of water transpired per plant, 

 however, was not proportional to the extent of leaf surface. Blackhull 

 kafir and Dwarf Blackhull kafir always had the lowest rate of transpira- 

 tion per unit of leaf surface in the experiments in which these plants 

 were used. All the varieties of corn used always transpired more water 

 per plant during any given period than any of the sorghums. Their rate 

 of transpiration per unit of leaf surface was, with the exception of the 

 kafirs, always much lower than that of the sorghums. The rate of trans- 

 piration per unit of leaf surface for feterita. Dwarf milo, Freed's sorgo, 

 and Red Amber sorgo was much higher than that of the corn plant under 

 the same conditions. This difference in the transpiration rate of corn 

 and the sorghums was more marked when the plants had reached their 

 full leaf development and the difference in leaf surface of these plants 

 had reached a maximum. The difference in the transpiration rate per 

 unit of leaf surface was also more evident under severe climatic condi- 

 tions than under conditions where the evaporation was low. 



The results of these experiments with com and the sorghums seem to 

 indicate that in most cases a small leaf surface is the most important 

 factor in reducing the loss of water from these plants. The corn plant 

 is not capable of supplying its large extent of leaf surface with a suffi- 

 cient amount of water to satisfy the evaporating power of the air, and 

 as a result its rate of transpiration per unit of leaf surface falls below 

 what it would be if the needed amount of water was supplied. The 

 sorghums, on the other hand, with their small leaf surface are able to 

 supply water in amounts sufficient to satisfy the evaporating power of 

 the air and, as a result, their rate of transpiration per unit of leaf surface 

 is higher than that of the corn. 



