in DEVELOPMENT AND ENVIRONMENT 59 



there is little profit in discussion of the phenomenon. It 

 should be mentioned, however, that so far as the avail- 

 able data go the cause seems certainly to be a form of 

 Thermotoxy, local in, and peculiar to, the particular 

 growing point. The differences between the various strains 

 thus are reduced to a specific susceptibility to thermic 

 effects, either in the form of increased " ^-production," or 

 deficient "x-destruction." The view does not claim to 



5-0 



< 



Af. 



K. 



C. 



\ 



\ 



Weeh June July 



ending 11 18 25 2 5 



August September October 



16 23 30 6 13 20 27 3 10 17 24 1 8 15j 



FIG. 43. SPECIFIC GKOWTH-HABIT. 

 Mean growth curves for central axis from various families in same year and 



on same plot. 



K. King Upland. S. Sultani. Af. Afifi. a'. Afifi, stunted plants only. 

 C. Commercial Ann in field crop. 



be an explanation, but it at least offers the prospect of an 

 answer to the question. 



Leaving these specific differences, and confining our 

 attention to the Afifi type of growth curve just figured, 

 which is fairly representative of the Egyptian cottons, we 

 can return to the effects of the environment proper. The 

 curve showing the mean growth per day of the terminal 

 bud of ten plants of Afifi (Fig. 30, growth), from 

 which we have already demonstrated the effects of 

 night-temperature, now becomes still more interesting. 

 After June 15th there is a slight indication of a 



