546 



Dr. J. C. Willis. On the Lack of 



the remark which I have already made* about the endemic species of Ceylon, 

 that (p. 13) "in general they have characters which are, so far as one can 

 conceive, useless in the struggle for existence ; they occur in places where 

 that struggle cannot have been very keen, or between very large numbers ; 

 they often occur alongside of their most nearly allied species, and very often 

 the differences in character are such as can hardly conceivably have arisen 

 by the selection of infinitesimal variations." The whole argument of that 

 paper should be read in connection with this, as it produces evidence 

 to the same end from a study of quite a different nature from that here 

 dealt with. 



Absence of Adaptation. — By a consideration of all the facts which have been 

 brought forward, we are thus forced to the conclusion that as there are not, 

 and have never been, any changed conditions to which these families have or 

 had to be adapted, there cannot have been in them any adaptation to changed 

 conditions after the first adaptation which enabled them to live on the rocks in 

 running water. The whole of the extraordinary morphological changes 

 through which they have gone are without any adaptational significance 

 whatever. The conditions of life under which T. ramosissima exists are 

 the same as those under which the rest of the families exist, and have 

 always existed since the evolution of the families began. In spite of the great 

 variety of form and structure, it is impossible to say that any one form is better 

 suited to the conditions of life than any other. The most " primitive " forms, 

 Tristicha and Podostemon, which have neither flattened shoot-thallus nor 

 root-thallus (except in one species of Podostemon, which perhaps should form 

 another genus) are the most widespread and the most common. 



It may be objected, perhaps, that the modification and adaptation to the 

 simple change of conditions involved by getting into the water is still going 

 on, and is enough to account for all the modifications that the families have 

 undergone. However well A may be adapted, it is of course obvious that B 

 may be better adapted. But if it requires the evolution of two whole families 

 with 30 genera and over 100 (perhaps over 200) species of the most various 

 form to meet this need, we have a very remarkable case before us, when we 

 consider that the first founders of the families must have been adapted to life 

 in running water, or the families could never have commenced. If this were 

 to be the case, we should expect enormously greater variety than actually 

 exists among the other plants of the vegetable kingdom. 



As has been pointed out, the most obvious feature in these plants where, if 



* Willis, " Some Evidence against the Theory of the Origin of Species by Natural 

 Selection of Infinitesimal Variations, and in Favour of Origin by Mutation," ' Ann. 

 Perad.,' vol. 4, p. 1 (1907). 



