Adaptation in the Tristichacece and Podostemacece. 547 



anywhere, we should expect adaptation, viz., the attachment of the seeds to 

 the rocks, shows none, except in one species only, and that the most highly 

 modified species in the whole family. Unless the haptera be an adaptation, 

 this is the only " adaptation " in the whole group, and if it takes all this 

 amount of evolution to get to one adaptation, there cannot be much selection 

 of advantageous variations. The morphological changes in these plants are so 

 large and striking that if there were any adaptation involved in them, there 

 would surely be some evidence to prove it, but there is none, and in all my 

 work on these plants I have not knowingly suppressed any evidence one way 

 or the other, or failed to put down anything that I have observed. 



Not only so, but the forms that are most like the common ancestors, and 

 possess none of the thalloid structures of the more bizarre genera, viz., 

 Tristicha and Podostemon, are much the most widespread and the most 

 common. As with the Dilleniacea^ and other orders instanced in my previous 

 papers, it is much simpler to regard these as parent genera which have split 

 off the others by mutation in different places. Everywhere they live together 

 with the more complex and modified forms, and in equal abundance. None of 

 the latter have one quarter of their range. 



Again, the more complex forms have flowers which are modified in a 

 direction that can only be looked upon as disadvantageous, if anything. I have 

 already gone into this question in another paper, and need only refer to it 

 here. By no conceivable advantages could the flowers have been the subject 

 of natural selection. 



There is no adaptational need for the complex forms ; if they are better 

 suited to the general conditions of life of the orders, there is nothing to prove 

 it, and they are not a conspicuous success, except in places that happen to 

 prove exactly right for them, as for instance Lawia zeylanica in the shallow 

 streams of the Bombay Ghats. The evidence of the local endemic forms is 

 also against this view of still-progressing adaptation. 



The conditions of life, as has been pointed out, are as nearly as possible 

 absolutely uniform, much more so than in other water plants, which have a 

 certain amount of soil differences, competition with plants of other families, 

 and so on, to face. So great is the destruction of seed before germination in 

 these families that until quite late in the season there is usually ample space 

 upon the rocks, so that there can be but little competition between them for 

 space. Competition for food cannot exist in water running so rapidly. 



The only " adaptation " that can be conceived of as going on in these plants 

 under these circumstances is to the ever-present force of plagiotropism, but if 

 this be admitted, it is also admitted that there can be definite evolution- 

 factors, which it is one of the objects of this paper to demonstrate. Adaptation 



