152 



THE COTTON PLANT IN EGYPT CHAP. 



of change in growth-rate, or as we have formerly inter- 

 preted this change the liability to thermotoxy. 



It was expected that a fourth factor would be found 

 operative in F 2 , &c., namely, the habit of branching, but 

 all heights and growth-habits appear to be distributed 

 evenly throughout all the branch-types, from plants with- 



/ Sultani 



June July 



Date 18-2 16 



30 



FIG. 56. GROWTH OF STEM. 

 Parents F! of an ^Egypto-Upland cross. Means of families. 



out monopodial branches at all,* up to plants in which the 

 main axis was scarcely recognisable. f 



The heights of the F 2 plants, are therefore dependent 

 on the three components first enumerated, but although 

 we have described them as " factors," they may be each 

 the resultant of more than one factor in the Mendelian 

 sense, as is the colour of the petal. Within the limits of 



* See Leake, H. M., (2), (3), and W. L. B. (5), (8), (15). 

 t Cf. Bateson, W., in Lathyrus. 



