318 THE LIFE OF THE PLANT 



the kind. Its other great advantage consists in 

 turning to its own account one of the strongest 

 objections which former supporters of the theory of 

 the variability of organic forms were unable to over- 

 come. This objection consists in the absence of transi- 

 tional forms between really good species. In fact, if 

 species are related to each other there must exist links 

 between them, some transitional forms. To this Dar- 

 win's theory says : such forms must indeed have existed, 

 but they have disappeared in course of time, and their 

 disappearance is one of the necessary results of the 

 struggle for existence and of selection. Before entering 

 into this question let us observe that an entirely false 

 representation is very often made of the transitional 

 form which connects two other forms. Such a form is 

 generally considered to be the middle form in the literal 

 sense of the word, a form which contains in itself the 

 attributes of both the forms which it links together ; 

 whereas in reality it may be almost entirely lacking in 

 the characteristic attributes of either of them. Very 

 often objections of the following kind are raised: if 

 the birch and the oak are related to each other show us 

 an organism that would be half one and half the other. 

 In all probability such an organism has never existed 

 in Nature. Organisms that exist to-day are related 

 to each other not because they may have originated the 

 one from the other, but because they proceed from 

 common ancestors ; and very probably had we found the 

 real link between two contemporary forms, i.e. the form 

 of the ancestor upon which their relationship is founded, 

 we should not have recognised it as such, because it 

 would have presented in very slight degree, if indeed at 

 all, the characteristic attributes of its two descendants. 

 Let us take an example from among cultivated plants. 

 The cabbage, for instance, is distinguished by remark- 

 able variety in the development of its organs ; in some 

 kinds of cabbage the head is composed of thickened 



