CHAPTER X 



THE THEORY OP WATERING 



§ 40. Why must we pay special attention to the watering 

 of plants ? 



After having examined the structure and function of the stem 

 and leaves, we must consider the conditions which conduce to 

 a normal development of these organs. We have already dealt 

 with the subject of transplanting, and assuming that the roots 

 will find a requisite amount of food material in the soil, we 

 must consider how the supply of water should be regulated to 

 ensure the continued activity of all the organs of the plant. 



It is a fact that the older a gardener grows the more care 

 he takes with the watering of his plants ; for year by year his 

 experience teaches him more definitely that careless watering 

 is the cause of an uncommonly large number of diseases of 

 plants. 



The difficulty in watering lies in the fact that plants require 

 various amounts of water according to their species, their age, 

 their situation, the season of the year, and their actual state of 

 health or development. The amount of water which is suffi- 

 cient at any given time may be very much too large a month 

 later, and may therefore cause considerable injury. Above all 

 things, we must remember that the tpanspiration from the leaf 

 surface is not a merely mechanical, but a physiological process, 

 and as such is regulated by the activity of different internal 

 organs, just as much in the case of plants as in that of animals. 



It is, of course, true that the conditions which increase the 

 transpiration of an inanimate object in general accelerate the 

 transpiration of plants, but this is by no means always the 

 case. 



The fact that the transpiration of living plants varies gene- 



