IN THE TROPICS : 111. 



123 



Thus, of determinable cobs, 7 showed 50 per cent, or less of 

 black grains, whilst 5 (including the two with black grains 

 only) showed a very much higher proportion. Among the 

 F2 grains from which these plants were grown, 25 were expec- 

 ted to be homozygotes (b x b) and 32 to be heterozygotes. 

 This is not far from the proportion 5 : 7 found between the 

 two groups as distinguished above. 



2. Offspring of F2 Series 2. (White Dent x Black Mexican) x (White 



Dent x G. W. S.) 



Expt. 43.— Offspring of while grains. 



21 plants out of 29 produced white grains only, the remainder 

 producing some black grains in addition. The expected pro- 

 portion of homozygote grains among the whites in F2 was 50 

 out of 67. Tn the case of 4 plants the proportion of black 

 and white grains was determinable. 



Expt. 44. — Offspring of black grains. 



17 plants all showed a considerable proportion of black 



grains in addition to whites. The actual proportion was 



determined in seven cases. 



Table 20. 



Total 



815 



869 



1,684 



48-4 



516 



Considering the individual numbers obtained in Expts. 

 43 and 44, we notice that the proportion of blacks among the 



