66 THE COTTON PLANT IN EGYPT chap. 



frequently; bears no relation whatever to the latter. Hence, 

 the variations in form of the boiling curve have to be 

 studied principally in terms of " shedding." 



In order to ascertain the shedding-curve, unless sufficient 

 assistance permits of direct measurement, we have to sub- 

 tract the boiling curve from the flowering curve, allowing 

 a certain interval for the maturation of the flower into a 

 boll. This period is variable, its length being in the first 

 instance speciQc. Thus, quoting again from the same 

 three families, at Cairo, King Upland has a mean matura- 

 tion period of forty-two days, Egyptian Sultani has a mean 

 period of fifty-one days, while the Afifi strain takes forty- 

 eight from the day when the flower opens till the day 

 when the boll cracks and discloses the contents. The 

 figures are determined by labelling single flowers with the 

 date on which they open. Apart from these specific 

 difiierences, which are, after all, only the mean expression 

 of numerous environmental influences acting on specific 

 organisms, we find variations in this period on individual 

 plants. Flowers which open on the same day and on the 

 same plant may difi'er by two or three days in their 

 maturation-period ; we must be content for the present to 

 describe such difi"erences as due to chance. Further, it 

 was first pointed out by AUard that in the United States 

 the maturation period became longer as the temperature 

 fell, so that the late bolls took longer to develop ; he 

 pointed out, as a curious example of the practician's 

 unreliability in practical matters, that the belief of the 

 farmer holds to the exact converse. The maturation 

 period is eight days longer in the middle Delta than at 

 Cairo. 



Since the mean for the standard Afifi strain at Cairo 

 lies at forty-eight days ±3 per cent., we shall not intro- 

 duce any serious error if we plot the mean shedding curves 

 of this strain by subtracting boiling from the flowering of 

 seven weeks previously. Such a subtraction-result is not 



