The Origin of Species 339 



tain desired qualities, but also to disturb the equilib- 

 rium of the species and induce wider varia- 

 tion, which may thus be taken as the basis for 

 selection. 



Aberrant Hybrids. Hybrids between two dis- 

 tinct species are usually intermediate in character 

 between the parents, but this is not always the case. 

 Sometimes one or the other parent is prepotent, 

 or certain parts may be inherited from one and 

 some from the other. Thus the flower of the hybrid 

 may resemble one parent, and the leaves the other. 

 Sometimes, however, the results of hybridization 

 are most unexpected, and the hybrid differs mark- 

 edly from both parents. This is the case in the 

 Primus blackberry, produced by Burbank from the 

 crossing of a wild California species, Rubus ur sinus 

 and R. cratccgifolius from Siberia. The hybrid 

 differs strikingly from either parent, and comes true 

 from seed, and might very well be described as an 

 entirely new species. Burbank has obtained similar 

 results in hybrid walnuts, produced by crossing the 

 native California walnut with the English walnut 

 and the black walnut of the Eastern States. In 

 every case the hybrid was distinguished by its ex- 

 traordinary vigor, growing with wonderful rapidity, 

 and far surpassing either of the parents in this 

 respect. Moreover, in many cases the nuts produced 

 by the hybrid were much larger than those of either 

 parent. A cross made by Burbank between a yellow 

 and a white poppy resulted in a flame-colored flower, 



