vii.] ORIGIN OF PARASITISM 67 



chlorophyll disappears, and perfect parasitism is 

 again recovered. 



That the power to become parasitic is a 

 general one seems obvious from the fact that 

 parasites occur in widely different orders ; but 

 why some roots when in contact with others are 

 stimulated by the latter into producing suckers, 

 rather than vice versa, or why they are not 

 mutually parasitic, is as obscure as the answer 

 to the question why some marsh plants have 

 become insectivorous, while others associated 

 with them have not. 



The point, however, which may be insisted 

 upon is, that parasitism is a consequence of 

 organic irritation, as described in cow-wheat. 

 This, when once fully set up and continued for 

 generations induces a hereditary predisposition 

 to parasitism ; as seen in many of the tribe 

 Euphrasiece of the order Scrophularinea. Then, 

 again, by further degradation in the structure 

 of the parasite, as in all which are devoid of 

 chlorophyll, it becomes a fixed, hereditary and 

 absolutely necessary condition of life. 



There would seem to be an impossibility 

 in applying natural selection to account for 

 all the above described details of parasitism ; 

 for, if it be contrary to evolution to allow the 

 first formation of haustoria to be in anticipation 

 of their use, for such would be teleological ; 

 then it must be those seedlings which had 



