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THE AMERICAN NATURALIST [Vol. XLII 



upon normal plants. Those abnormal characters all be- 

 came connate with the normal characters after the estab- 

 lishment of their heredity, but they never became sys- 

 tematically correlated with them. 



The questions that here almost crowd themselves upon 

 one's attention are, how have those wayward phenogams 

 accomplished their departures from normal conditions, 

 and what was their incentive for doing so f Doubtless in 

 all cases the chief incentive to parasitism, after the opera- 

 tion of an unknown predeterminate cause, has been food- 

 lust, the instinctive object of the plant being to procure its 

 nourishment in an immediately available form. The fol- 

 lowing respective references to the seven groups of phe- 

 nogamous parasites are necessary to the present subject, 

 but they show how difficult it is to make any sufficient 

 answer to the first of those questions. 



In pursuance of the subject as just indicated it may be 

 suggested that the members of group I, which prey upon 

 the roots of other plants and are only partially parasitic, 

 originally acquired their habit of underground pilfering 

 by the accidental charing together of the tender roots of 

 closely-growing plants, which brought bared, new-formed 

 cells into contact at the crossings of the roots. Vital 

 union of the roots at those points, such as takes place in 

 grafting, having resulted, the more vigorous plant be- 

 came the parasite by withdrawing a portion of the partly 

 elaborated food-sap from the weaker one. It is plain, 

 however, that thousands of cases are constantly occurring 

 of similar contact of growing roots which do not result 

 in parasitism. Both the normal and abnormal charac- 

 ters are possessed by every individual plant of every 

 species pertaining to group I, and they are thus, all to 

 the same extent, distinguished from normal plants and 

 from all other parasites. In no case is one of this sim- 

 plest of the forms of phenogamous parasitism known to 

 show any inclination to greater complexity, or to abandon 

 its present restricted parasitic habit. The heredity of 

 that habit is permanent, and no known fact suggests that 



