TRANSPIRATION 179 



also is an interesting subject tliat should be more 

 fully investigated in the future. 



Ninth, the vigor of growth of a crop appears to 

 have a strong influence on transpiration. It does not 

 follow, however, that the more vigorously a crop 

 grows, the more rapidly does it transpire water, for 

 it is well known that the most luxuriant plant growth 

 occurs in the trojDics, where the transpiration is exceed- 

 inglj^ low. It seems to be true that under the same 

 conditions, plants that grow most vigorously tend to 

 use proportionately the smallest amount of water. 



Tenth, the root system — its depth and manner of 

 growth — influences the rate of transpiration. The 

 more vigorous and extensive the root system, the 

 more rapidly can water be secured from the soil by 

 the plant. 



The conditions above enumerated as influencing 

 transpiration are nearly all of a physical character, and 

 it must not be forgotten that they may all be annulled 

 or changed by a physiological regulation. It must 

 be admitted that the sul^jectof transpiration is )^et 

 poorly understood, though it is one of the most im- 

 portant subjects in its applications to plant produc- 

 tion in localities where water is scarce. It should 

 also be noted that nearly all of the alcove conditions 

 influencing transpiration are beyond the control of the 

 farmer. The one that seems most readily controlled 

 in ordinary agricultural practice will be discussed in 

 the following section. 



