306 Mr Biffen, 



other parent. The F 1 was awnless, showing that this condition, 

 as in the case of the wheats, is dominant, whilst the F 2 consisted 

 of hooded and awnless individuals. The awnless parent is a variety 

 in the sense of the word as used by de Vries, and it is one of very 

 recent origin, yet it is dominant over the older type. 



The crosses between varieties in which one parent has dense 

 the other lax ears have now to be considered. In the case of 

 wheat, where these characters are also present, Spillman showed 

 that the F 1 was intermediate between the parents in this respect, 

 and that in the second generation the normal segregation occurred, 

 resulting in the production of lax, intermediate, and dense ears in 

 the proportion of 1 : 2 : 1. In the barleys I have examined up to 

 the present the F 1 is also intermediate between the parents in the 

 density of the ears. When, however, one attempts to separate the 

 three expected types one can readily pick out many of the two ex- 

 tremes, but numerous cases occur where one cannot say whether 

 any given ear should be classed as an intermediate or not. On 

 shuffling the ears and again attempting to separate them, a result 

 totally at variance with the former one was generally obtained. At 

 first I was under the impression that this was due to the difficulty 

 of correctly gauging the relative laxness and denseness by eye, so 

 I measured the length of the internodes, but the figures so obtained 

 did not fall into the three expected groups. On plotting curves 

 for a number of separate crosses with these figures on the base line 

 the explanation of these apparently non-conformable cases was 

 found. Where there were extremely lax and dense forms crossed 

 it was clear that the three separate curves existed, but the ends of 

 the curves corresponding to the lax and dense types were covered 

 by the curve of the intermediates. In cases where the difference 

 between the parents was less pronounced the overlapping was so 

 great that the three curves fused into one, showing, however, on 

 either side a distinct secondary apex. The F 2 generation of the 

 cross between H. pyramidatum and H. decipiens may be taken to 

 illustrate this point further. The average internode length of the 

 parents was found to be 1/8 and 3"4 mms. respectively, that of the 

 F 1 32 mms. The measurements for the F 2 generation were as 

 follows : 



1-4 1-6 1-8 2-0 2-2 2-4 2-6 2-8 3-0 3-2 3-4 3-6 3-8 4-0 4-2 4-4 mms. 

 3 7 14 19 12 42 41 28 15 6 4 2 2 1 individuals. 



An individual ear measuring 24 mms. then may be either a 



true dense form or a heterozygote, and the distinction can only be 



made by sowing its grains and observing whether the progeny are 



constant or whether segregation occurs. This test has been carried 



out in the example quoted, and by separating the individuals in 



this way it was found that the splitting was normal, as it resulted 



in the production of two intermediates to one each of the lax and 



