Hybridization 145 



laburnum (Cytisus purpureus) into a stock of the yellow 

 (Cytisus laburnum). M. Adami, who made the graft at 

 Vitry, near Paris, about 1826, has left on record that from 

 it there sprang the existing hybrid. There can be no 

 question as to the truly hybrid nature of the latter. It 

 is, however, absolutely sterile, and is multiplied by grafts. 

 It bears three kinds of flowers some pink, others large 

 and yellow, others small and purple. That is to say, it 

 bore its own hybrid flowers, also those of its two parents, 

 and the leaves and ramifications of the parts of the tree 

 which bore these three kinds of flowers were likewise of 

 the same three kinds and could be distinguished even in 

 winter. 



Strasburger made a careful cytological study of Cytisus 

 Adami, which has been retained in cultivation ever since 

 its origin some eighty years ago. He came to the con- 

 clusion that Cytisus Adami was a real sexual hybrid and 

 not a graft-hybrid. He thinks that if the latter were 

 true, the nuclei of the hybrid would show a double number 

 of chromosomes. This, of course, implies that in hybrids 

 arising otherwise than sexually, assuming that a nuclear 

 fusion would precede the formation of such a hybrid, 

 there would be no reduction division of the nuclei com- 

 parable to that which normally occurs before the fusion 

 of the sexual cells in normal fertilization. 



Nemec, however, thinks that a reduction division 

 does occur and there is, therefore, no reason to expect 

 an increase in the number of chromosomes in the cells 

 of the hybrid. If such a reduction does occur, Cytisus 

 Adami would show the same number of chromosomes as 

 C. laburnum, which has the same number as C. purpureus. 

 L 



