Wire Stem of Cabbage 



57 



These experiments indicate that sand may even be detrimental. 

 Whether or not this is actually so in every case cannot be stated positively 

 until further experimental work has been done. 



Another experiment was performed to determine the influence of a 

 surface layer of sand on the evaporation of water from the soil. Fine 

 quartz sand was used, instead of the coarse sand employed in the previous 

 experiments. Four culture vessels were used in each of five moistures. 

 All the cultures were watered through glass tubes extending to the bottom 

 of the vessels. About fifteen seedlings were transplanted into each jar as 

 before, and were allowed to grow for a week. Inoculations were then made, 

 and immediately the surface of two of the culture vessels in each moisture 

 series was covered with a layer of sand about one-quarter inch deep. 

 The moisture content was kept constant by weighing every other clay and 

 adding the required amount of water. During the entire experiment the 

 sand-covered vessels lost only about half as much water as did those that 

 were not covered. It was thus to be expected that the covered vessels 

 were the more ideal for the development of the disease, and later observa- 

 tions demonstrated this to be the case (table 19 and figure 15). 



TABLE 19. 



Influence of a Layer of Quartz Sand on the Surface of the Soil, on 

 Damping-off Caused by Corticium vagum B. & C. 



* Percentage of maximum retentive power of soil as determined by the Hilgard method. 



