i6 



THE COTTON PLANT IN EGYPT chap. 



20 mm. 

 10 mm. 



Mean Growth per day on Ten Afifi Plants, (main axis) 

 Sown ,— ^ 



Date of Watering W 



Flowering Mean 



Shedding Growth 



Boiling mm, 



a p.p.p.d. per day 



Co 0-5 — 



Records of Individual Plant shown in Fig. 37. 



Sown 



I Germinated 



grou)tj'^«-« 



Date 



-I — i ' 1 i TT 

 April 



May 



I I 1 I 

 June 

 28 1 



Fig. 30. — The Plant and the 



are both obviously greater than that of the dry soil. The 

 magnitude of this daily change in soil-temperature 

 diminishes with increasing depth, and is negligible below 

 50 cm. Thus the root-tip in the early stages of germina- 

 tion is subject to great variations in temperature, but 

 after the root has grown some 15 cm., the temperature is 

 constant, except for the annual change. At a depth of 

 50 cm. the temperature is approximately 17° C. at the 

 beginning of March, rising to about 25° C. in the 

 summer. 



The localisation of the optimum sowing-date will be 

 discussed later, in connection with the date of the first 

 flower. For the present it suffices to notice that sowings 

 in the middle of February near Cairo will take twelve 

 days to show the cotyledons above ground, while identical 

 sowings made in the middle of April may appear in five 

 days, temperature being the limiting factor. The sowings 



