64 THE COTTON PLANT IN EGYPT CHAP. 



of this result is the inevitable deduction that two cotton 

 plants can occupy more than three tons of soil with 

 their roots by the end of July. In making a further 

 comparison of the tank-plants with those sown in field- 

 conditions, we find in the latter a similar arrest of the 

 rising curve, which is probably to be explained in the 

 same way, as due to root-limitation, formerly discussed. 



Such variations as those just mentioned may be produced 

 within the same pure strain in at least two ways ; either 

 by checks upon the growth of the flowering branches, 

 or by shedding of the flower-buds. The latter falls 

 into the same category as the shedding of flowers 

 or bolls, but should be mentioned here as a possible 

 source of variation in the flowering curve. With 

 certain strains, notably one bred by the author from 

 an Egypto - American cross, this effect is marked 

 very strongly ; some plants, otherwise identical with 

 their neighbours, shed their flower -buds just before 

 opening them, while their neighbours retain them. The 

 first produce a scanty flowering curve, the others a gigantic 

 one. Neither, however, ripen any early bolls, and the 

 distinction appears to be due entirely to accidental root- 

 differences. 



Another important factor which modifies the form of 

 the latter part of this curve is the water-table. The 

 coincidence in time between the contact of the roots with 

 the water, and the rapid cessation of flowering, is shown 

 very clearly in records from families sown on different 

 dates, the idiosyncrasies of each family being obliterated 

 when this contact takes place ; on continued rising of the 

 water the flowering curves all coalesce at or near zero. 

 The field crop records taken at Giza show variations in 

 this respect as between 1909 when the flood was very 

 early, and the two "following years when the flood was late 

 (Fig. 45). 



These last records are of exceptional interest, as they 



