48 



Plant Physiology 



unfavorable conditions of the environment. The ability 

 of a plant to take water from the soil, moreover, will de- 



pend in large measure upon the ex- 

 tent of these simple organs. It has 

 been estimated that the surface of 

 the system in corn is increased from 

 five to six times by favorable root-hair 

 production ; in barley about twelve 

 times, and in Scindapsus about eight- 

 een times. 



31. Root-hairs and the water-con- 

 tent of the soil. - - It is only in ex- 

 ceptional cases that land plants de- 

 velop few or no root-hairs. In general, 

 where few are present, the plant will 

 wilt with a higher water-content of 

 the soil than when more are provided. 

 Root-hairs are considerably suppressed 

 j n ^he case o f corn? wheat, and other 



. . 



crop plants when the soil is saturated. 

 Nevertheless, many plants continue to produce such 

 organs in water cultures, even though the number of these 

 organs or the individual length of each may be greatly 

 reduced. In the soil so long as the plant does not wilt, 

 it appears to be generally stimulated to most abundant 

 root-hair production at a moisture content somewhat 

 less than that which will afford the highest yield. 



It is commonly assumed that darkness is an immediate 

 factor in the development of the root-hairs, but this as- 

 sumption does not appear to be sustained by experiment. 

 Relatively strong, diffused light with adequate water- 



FIG. 12. Root-tip of 



corn, diagrammatic. 



