IN THE TROPICS : ID. 



161 



The proportions of blue grains shown by these 32 plants 

 are indicated in fig. 3 by the dotted curve, which is con- 

 structed from the whole number of percentages in Tables 

 45 and 46 combined, whilst the unbroken curve shows those 

 from Table 45 only. 



The range of variation and the modal value will be seen to 

 be closely similar in the two cases, in spite of the fact that in 

 the parent cob of one series of plants blue was dominant 

 in every grain, whilst in the other only 24 out of a possible 

 50 grains showed dominance of blue. No explanation of this 

 remarkable result presents itself. 



Expt. 72. — Non-blue grains from the same F 2 cob (showing 

 24 per cent, of blue) gave rise to 34 plants. Of these, 20 showed 

 no blue grains at all, and with these must be reckoned 3 

 which showed only 1 or 2 blue grains. The remaining 11 

 cobs bore from 5 to 37 per cent, of blue grains, again noticeably 

 fewer than were born by the offspring of blue F 2 grains 

 from the same cob and of the same supposed constitution, 

 i.e., heterozygotes of the nature blue x white. 



23 out of 34 therefore of the non-blue grains of F 2 are shown 

 by the behaviour of their offspring to have been pure homozy- 

 gotes, whilst 11 were heterozygotes. That is to say the homo- 

 zygotes made up 51-4 per cent, of the total number of grains 

 on F2, whilst the expected number was 50 per cent. 



