224 Fertilisation and Hybridisation 



by a simple cut. And, if not by a simple cut, then at least 

 by a physiological splitting, which passes exactly between 

 the two parental groups and does not leave in one of them 

 any trace of the other. 



In this manner we have to picture to ourselves, in a 

 general way, the internal, invisible structure of the hy- 

 brids. The bearers of the characters of both parents are 

 intimately connected, and together dominate the visible 

 characteristics. But they are not, by any means, fused 

 into a new indivisible entity. They form twins, but re- 

 main separable for life. 



In all nature there is probably not another such beauti- 

 ful instance of splitting as the above-mentioned Cytisus. 

 But with lesser differences between the parents, splittings 

 of the parental types occur frequently in the vegetative life 

 of hybrids. Many horticultural plants, and especially the 

 bulbous plants, furnish instances thereof; peas, corn, 

 wood-sorrel, anagallis, oranges, and several others are 

 known instances. The fruits that are half lemon and half 

 orange, belong doubtless to this group. Among the hy- 

 brids of the common and the thornless thornapple (Datura 

 Stramonium) , individuals have been found, although very 

 rarely, that showed a similar splitting, and which even 

 bore on the same fruit armed, as well as thornless cells. 

 In my garden, I cultivated, for many years, a Veronica 

 longifolia which was a hybrid from the blue species and 

 the white variety, and correspondingly had blue flowers. 

 But from time to time splittings occurred ; either one single 

 spike bloomed white, or a few isolated white flowers ap- 

 peared on an otherwise blue spike. 



During the entire life, up to the time of the formation 

 of the reproductive cells this internal dualism manifests 

 itself in this way. Sometimes proofs of it are even found 



