23 



FiG. III. PEDIGREE OF CLAY AND MOSS BARLEYS. 



The development, or more properly the separation of the above two 

 barley types affords an excellent illustration of how selection en masse may 

 be effected. The only necessary condition in order that such separation 

 may be made is that different hereditary forms be present and that these 

 present differences in respect of the character sought. In the case in ques- 

 tion this success was due to the existence of different forms possessing differ- 

 ent specific head-densities. By the annual selection from each group of 

 those heads, the density of which approached most nearly that which was 

 desired, there was gradually eliminated the 'transgressive ' or 'overlapping ' 

 forms until at the end of the fourth year two groups representing the two 

 types mentioned remained. 



This explanation of the separation of the two barley sorts Clay and Moss, 

 affords an argument that at least some of our common varieties are composite 

 in character and are capable of being divided into their component parts 

 which in turn may possess different values. 



A similar example of how it may be possible to effect gradually a separa- 

 tion of two distinct types by mass-selection is to be found in an experiment 

 conducted some years ago at the Experimental Station at Tystofte, Denmark, 

 and described by Tedin (66 p. 23) in the journal of the Swedish Association. 

 The primary object of this experiment was to determine the comparative 

 values for seeding purposes, of large and small kernels in the case of barley 



