130 



WILLIAM H. BROWN 



Vicia faba Linn. Seedlings of this species, grown under the 

 lath shelter during the summer, had a normal appearance but 

 they were not able to bear the high evaporation rate of the open ; 

 it was found impossible to grow them under full sunshine. For 

 these experiments the plants were grown under the lath shelter, 

 behaving normally until they had attained a height of from 15 

 to 20 cm. After this, however, they wilted regularly during 

 the middle of the day. As will be seen from table 8, this was 

 the case even when the soil was saturated beyond its water hold- 

 ing capacity (31.4 per cent). After reaching this stage growth 

 practically ceased and the plants soon died. 



Table 8 gives the water content of the soil for plants about 

 15 cm. high, wilting under the lath shelter and in the house. All 

 of the plants under the shelter wilted at approximately the same 

 time, but with very different amounts of water in the soil. This 

 suggests that, in this case, the time of wilting may have depended 

 more on the rate of evaporation than on the moisture content 

 of the soil, and that the death of the plants a few days later may 

 have been due to excessive transpiration coupled with inade- 

 quate power of water conduction. 



TABLE 8 



Percentage of soil moisture at the time of wilting of similar plants of Vicia exposed 



to two different evaporation conditions 



