Experiments on the Hybridisation of Barleys. 305 



In addition there are a number of minor characters, so that it 

 is obvious that there may be an almost indefinite number of com- 

 binations. 



In order to simplify another problem we have in hand it has 

 been necessary to trace in some detail the inheritance of these 

 various characters. For the most part this has not proved a diffi- 

 cult matter, and few complications have been met with. Most of 

 the various characters segregate sharply from one another, and 

 form good examples of the allelomorphic pairs we are now so 

 familiar with. These pairs are as follows, the dominant character 

 being placed first in each : 



1. Trapped and naked grain. 



2. Brown, black, or purple paleae and white. 



3. Dark and light coloured grain. 



4. Trifurcate and normal awns. 



5. Narrow and broad glumes. 



6. Two-row and six-row. 



7. The decipiens type and two-row. 



8. The decipiens type and six-row give an intermediate. 



9. Lax and dense ears give an intermediate in the F 1. 



For the present attention need only be called to the more 

 complex cases. The first of these is provided by crosses between 

 the awned and trifurcate varieties. Tschermak has described one 

 example of such a cross, and he states that the awned form is 

 dominant over the trifurcate. In the four cases I have examined 

 the supernumerary flowers have always been present in the F 1, so 

 that it would appear as if the hooded or trifurcate form was 

 normally dominant over the awned. The F l's, however, differ 

 a good deal among themselves with regard to the position of the 

 extra florets. In one cross-bred they were practically sessile, as in 

 the parent, but in the other three they were borne on long awns 

 which were prolonged beyond them. In the subsequent generation 

 most of the hooded forms bore the extra floret on awns some three 

 or four centimetres in length. In many of these plants few of the 

 awns carried such fully developed extra florets as the parent. If 

 all of these partially hooded forms are to be reckoned as trifurcate 

 then there is good reason to consider the trifurcate condition as 

 dominant, for they occur in the proportion of three to one of the 

 normally awned forms. On the other hand, it may be that the 

 F 1 should be described as an intermediate, in which case the 

 partially hooded types should occur in the proportion of two to 

 one of the awned, but the difficulty of deciding between fully and 

 partially hooded ears is too great for one to separate the forms 

 satisfactorily. This can, however, be determined in the following 

 generation. One other cross between a hooded variety may be 

 mentioned here. In this case an awnless variety was used as the 



VOL. xm. pt. v. 21 



