WATER CONTENT OF PLANT AND SOIL, 



39 



Tbe colder air retarded some-what the growth of plants in 

 Case I, and its effect was to increase the average of non- 

 available water to the extent of 0.6 per cent. The plants in 

 Case I were longer in dying than those in Case III because 

 in the lower temperature the evaporation took place more 

 slowly. The average time of dying in Case I was 19 days, 

 in Case III 25 days. The slower evaporation of water tended 

 to allow the plant more time for adaptation, lowering the 

 physiological water limit and counteracting the effect of the 

 cooler temperature. This being taken into consideration the 

 difference in the average from the two plants would be the 

 more significant if it were not so small. The difference 

 caused by tbe cold was not noticeable in the case of barley and 

 oats, but was quite striking in the case of corn and beans. 

 This bears out observations of farmers to the effect that the 

 small grains grow well during a cool spring, but corn is re- 

 tarded. 



3. Effect of Increased or Decreased Humidity, when excessive. 



The plants grown under the conditions of case IV, were 

 constantly in a humid air, even when the soil was deprived of 

 water in the determination of the physiological water. They 

 grew taller than those in the other cases. The leaves were 

 slightly larger, and the root system less extended than those 

 of the plants in the Cases I and III where the air was less 

 humid. Comparing the results with those from Case III, 

 the case with the normal conditions, the effect of the in- 

 creased humidity is readily seen. 



