306 Retrograde Varieties 



after pure fertilization. Mendel's law teaches 

 us to predict the difficulties, but hardly shows 

 any way to avoid them. It lays great stress on 

 the old prescript of isolation and pure fertiliza- 

 tion, but it will have to be worked out and ap- 

 plied to a large number of practical cases before 

 it will gain a preeminent influence in horticul- 

 tural practice. 



Or, as Bailey states it, we are only beginning 

 to find a pathway through the bewildering maze 

 of hybridization. 



This pathway is to be laid out with regard to 

 the following considerations. We are not to 

 cross species or varieties, or even accidental 

 plants. We must cross unit-characters, and 

 consider the plants only as the bearers of these 

 units. We may assume that these units are 

 represented in the hereditary substance of the 

 cell-nucleus bv definite bodies of too small a size 

 to be seen, but constituting together the chromo- 

 somes. We may call these innermost repre- 

 sentatives of the unit-characters pangenes, in 

 accordance with Darwin's hypothesis of pan- 

 genesis, or give them any other name, or we may 

 even wholly abstain from such theoretical dis- 

 cussion, and limit ourselves to the conception of 

 the visible character-units. These units then 

 may be present, or lacking and in the first case 

 active, or latent. 



