152 



THE COTTON PLANT IN EGYPT chap. 



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

 preted this change — the liabihty to thermotoxy. 



It was expected that a fourth factor would be found 

 operative in F.,, &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 



King 



June 

 Date 18 



Fig. 56. — Growth of Stem. 

 Parents F^ of an .lEgypto-Upland cross. Means of families. 



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

 main axis was scarcely recognisable, t 



The heights of the Fj 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. AVithin the limits of 



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

 t Cf. Bateson, W,, in Lathy'rus, 



