624 Validity of the Doctrine of Mutation. 
of an undoubted graft hybrid has, however, as yet been 
produced experimentally and, consequently, the charac- 
Fig. 140. Cytisus Adaini. A, A', bearing at I a bunch of 
twigs of C. pur pur cits \ P, H, and I. 
ters which such hybrids would have if they existed are 
not known and can even hardly be guessed at. Therefore 
