64 Diseases of Truck Crops 



for all life. Plants breathe through their leaves, 

 and, according to Whitney, x through the roots also. 

 Hence, cultivation is necessary not only to supply 

 air to the microorganisms in the soil, but also to 

 the roots of the crop. In the opinion of Whitney, 

 cultivation accomplishes a step further; by 

 stirring the soil we permit the escape of foul gases 

 given off by the plant roots as well as by the soil 

 organisms. 



Need of Water 



Plants to live must drink. This is one of 

 the most important considerations from the 

 trucker's point of view. It is generally sup- 

 posed that roots are fixed things in the soil, 

 receiving water and food material by capillary 

 action. This occurs only in very moist and 

 saturated soils. However, in dry seasons and 

 in dry soils the roots have to move down- 

 ward towards the water. This may be proved 

 by a simple ingenious experiment described by 

 Whitney. "If you take some soil from the 

 field with what we call an optimum amount of 

 moisture, or the best amount for plant growth, 

 put it in a tumbler, filling the tumbler about 

 half full, and put some dry soil on the surface, 



'Whitney, Milton, U. S. Depart, of Agr. Farmers Bui. 257: 

 5-35, I909- 



