CHAPTER II 



DEVELOPMENT AND ENVIRONMENT I 



THE physiology of a cotton plant growing under the field 

 conditions which obtain in Egypt may be conveniently 

 considered in two stages. During the first stage, which 

 includes the period from sowing to flowering, the plant 

 is mainly under the control of aerial conditions. After 

 flowering, in the middle of June (near Cairo), a critical 

 period ensues, during and after which the soil conditions 

 commonly provide the limiting factors. 



The subject is one of great interest, on account of the 

 stringent environmental conditions which prevail during 

 a great part of the Egyptian cotton-season. (See Figs. 

 30 and 33, Environment.) Thus, in the month of June at 

 Cairo the meteorological conditions are somewhat as 

 follows : Sun temperature maximum, 75 C. ; Clouds, rare ; 

 Shade temperature maximum, usually 34 C., at 2 p.m. : 

 occasionally 42 C. : minimum about 20 C., at 6 a.m. ; 

 Humidity, dropping to 20 per cent, of saturation, or even 

 less, during the day, and rising above 90 per cent, at 

 night ; Yv^ind, strongest by day. 



Such conditions result in xerophytic adaptions, unless 

 an ample water-supply is available, as it is in Egypt 

 through irrigation ; but we shall see later that even under 

 conditions of field cultivation, the cotton plant virtually 

 becomes a xerophyte every afternoon. After the month 

 of June, however, the increasing size of the plants 



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