CHAPTER III 



DEVELOPMENT AND ENVIEONMENT 11 



The second half of the development of the cottou plant in 

 Egypt may be conveniently subdivided into three stages, 

 though none of these have any definite boundaries. They 

 are, successively, the critical period, the water-table period, 

 and the autumnal period. The first of these three is little 

 more than an abstract term which has been found useful 

 in discussion, while the other two explain themselves. 



The chief feature of all three, though especially of the 

 first two, is that the main control of the environment has 

 been transformed from the air to the soil (Fig. 30). This 

 change can be seen clearly in the growth curve. During 

 the first period, under the modern conditions of Egyptian 

 irrigation, the plant can always be supplied with sufficient 

 water, but the adjustment of the water-supply becomes a 

 very delicate matter during the critical period, owing to 

 root-interference ; while excess of water is likely to be 

 present during the next period, partly from natural causes, 

 and hence reduction in the efi"ective root-system follows. 

 AVhen the sub-soil water period is very early, and con- 

 sequently overlays the critical period, the combination of 

 the two produces disastrous eifects, of which the 1909 

 crop was our worst example, through an early and high 

 flood. 



During these three periods the maturation of the crop 

 takes place. We arc chiefly concerned with the flower, and 

 with the boll which ripens from it, though also with the 



