IN THE TROPICS : III. 173 



explanation, as has been the case with other plants when more 

 precise methods were employed. This being understood, we 

 may pass on to describe the phenomena actually seen in the 

 present instance. 



The account may be somewhat simplified by using a special 

 notation. We may write : — bb for homozygote blue (or black) ; 

 wb for heterozygotes, blue (or black) blue in appearance ; 

 w(b) for white grains among the offspring of which blue 

 reappeared, i.e., heterozygotes white in appearance; and ww. 

 for homozygote white. 



In Fi from Black Mexican crossed with white dent — 



b x w gave wb. 



w x b gave wb and w(b). 



The behaviour in F 2 may be stated as follows : — 



(1) wb x wb gave bb wb w (b) and ww 



' ~3 : 1 



(2) wb x w gave wb w(b) and ww 



r : 1 



(3) w x wb gave wb w(b) and ww 



^T~ : 1 



The view embodied in this table is supported by the follow- 

 ing evidence derived from the next generation (F 3 ), in which 

 all the different kinds of grains were sown and the plants 

 again fertilized with pollen from a white strain. Under these 

 circumstances — 



ww (white) X w yielded only white offspring. 



w(b) (white) x w gave either (1) 50 per cent, black, or (2) 



some number of black less than 50 per cent, 

 bb (black) x wgave either (1) all black, or (2) a percentage 



of black much higher than 50, e.g., 80 per cent. 

 wb (black) x wgave approximately 50 per cent, of blue, or 

 sometimes slightly less. 



It will be seen that certain assumptions are here made, of 

 which the most questionable is the supposition that 80 per cent . 

 of blue in the offspring indicates a homozygous parent.* A 



* But the assumption is rendered almost a certainty when it is found 

 that all the white grains (20 per cent.) of such a cob include some 

 blacks among their offspring. 



