Ill DEVELOPMENT AND ENVIRONMENT 67 



precise, but it is very useful in cases where direct 

 shedding-records have been impossible. 



The shedding curve. — We have just seen that the 

 boiling curve, which represents not only the distribution 

 but also the size of the ultimate yield of the plant, and 

 hence of the area, is in reality the flowering curve modified 

 by shedding. This shedding process thus becomes a 

 matter of great economic importance. More than this, 

 the shedding of an organ of the plant is a phenomenon of 

 great interest from the general scientific viewpoint. The 

 fact that removal of a few roots should cause the abscission 

 of leaves or flowers, quite automatically, leads directly to 

 consideration of the complex interaction of stimuli 

 necessary to produce such transmission and conversion of 

 cause into effect. 



The term in common use to describe the process under 

 discussion is " boll-shedding." It is not altogether satis- 

 factory, since the organs shed by the plant are chiefly 

 flowers shed three or four days after opening, and hence 

 only described as bolls by courtesy. Ripening bolls, up to 

 two centimetres in diameter, may be shed, but this is less 

 common. In addition, there may be extensive shedding 

 of unopened flower-buds, and the fall of the leaves belongs 

 to the same general category. Consequently, the general 

 term "shedding," while sufficiently descriptive, is more 

 truthful. 



The composition of the sheddings actually gathered from 

 the ground beneath a field plot of more than a thousand 

 plants in 1910, at Giza, is shown in Fig. 46. Shed leaves 

 were not counted, but the diagram shows that flower-buds 

 may be shed even before the opening of the first flower, 

 that the majority of the sheddings are flowers which have 

 been cut ofi" before they had definitely " set " their ovaries, 

 while the percentage of true bolls of various ages up to 

 three weeks old is only noticeable in the autumn. 



The act of shedding is, of course, under the control of 



F 2 



