in DEVELOPMENT AND ENVIRONMENT 71 



aerial organs of a certain size, is now insufficient to cope 

 with the normal water-loss of those organs. They in their 

 turn reduce their water-loss to meet the new conditions by 

 stomatal closure, but the general metabolic disturbance, 

 due to demolition of the delicate balance between root and 

 shoot, produces shedding. We have already seen how 

 delicate that balance is, when noting that plants would 

 grow in sunshine if a few leaves were removed. Here we 

 are dealing with the converse. 



Much more experimental work is needed on -such points 

 as the permissible degree of desiccation or of saturation in 

 various types of soil, on the rate of renewal of soil water 

 to a root-dried zone, and so forth, but the main principles 

 of the matter are now fairly clear. 



In light soil, which has a low power of water retention, 

 it would seem from consideration of the shedding curve 

 that frequent light waterings are necessary. This practice 

 might, on the other hand, be unnecessary, if not injurious, 

 in a heavier soil, with a higher capacity for holding water. 



A mode in the boiling curve may actually originate 

 from a falling flowering curve, if all the. flowers had been 

 held during one week, so that a heavy crop of bolls is 

 picked seven weeks later (Fig. 30). 



Some interesting shedding curves have been obtained 

 by the author from land arranged * in three terraces, at 

 half-metre differences of level. The purpose of this 

 arrangement was to ensure differences in the time and 

 intensity of the effect of rising sub-soil water ; the lowest 

 terrace was first affected, the highest last ; the water-table 

 in the lowest one almost reached the surface of the soil, 

 while in the highest it left a metre of normal soil. 

 The method is not ideal, on account of the soil disturb- 

 ances entailed, even when the top half-metre of soil is 

 carefully replaced on each terrace ; the remainder of the 



* In collaboration with Mr. Hughes. 



