1913. 



PUBLIC DOCUMENT — No. 31. 



67 



mal renders it more susceptible to winter killing, topburn and 

 even fungous infection. Lettuce, for instance, will burn more 

 quickly when the tissue contains more than the usual amount 

 of water, and mildew and rusts are more common on plants 

 with a relatively high water content. 



The object of our experiments in growing plants in different 

 percentages of soil moisture was to determine what influence 

 soil moisture had on the development of the plant, with special 

 reference to susceptibility to burning from hydrocyanic acid 

 gas. We used cucumber plants, as before, growing them in 

 small, galvanized iron pots holding about l^/o kilograms of soil. 

 The soil was the greenhouse type, containing considerable or- 

 ganic matter, with a water-retaining capacity of 47 per cent. 

 The total water-retaining capacity of the soil in these experi- 

 ments was regarded as 100 per cent. The various soils in the 

 pots were maintained at 10, 20, 50 per cent., etc., of the total 

 water-retaining capacity. 



After reaching a certain degree of development under green- 

 house conditions the plants were placed in a tight case, as in the 

 preceding series of experiments, and treated with .007 grams 

 of cyanide per cubic foot, as before. Aft(3r treatment the plants 

 were taken out of the case and left for further observations. 



Table II. — Showing the Effects of Different Percentages of Soil Moisture 

 on the Growth of Cucumber Plants and their Susceptibility to Burning 

 from the Use of Hydrocyanic Acid Gas. 



Experiment I. — • Duration, June 5 to June 20. 

 [Measurements in centimeters.] 



Note. — Nos. 1, 2 and 3, no burning; Noa. 4 and 5, burned. 



