52 THE ORIGINATION OF PARASITISM. 



or as indicating absence of the spirit of inquiry. The inheritance of ac- 

 quired characters has been the subject of much observation and some experi- 

 mentation, but in general the problems in this and in the study of adaptive 

 arrangements are involved, and the experimental tests demanded are diffi- 

 cult of organization and necessarily require periods of time for their com- 

 pletion which would include a large proportion of the active period of any 

 individual worker. 



Furthermore, it is to be seen that experimentation of the kind demanded 

 in such work must be carried on in field laboratories, or in places where 

 the biotic elements may be handled under habitual conditions of environ- 

 ment. The tendency of the naturalist to carry his tools, his laboratories, 

 and his apparatus to the home of the organism he wishes to study is one 

 which is gaining in favor, and rightly so, since it will undoubtedly yield 

 results of importance on many subjects which have eluded us hitherto. 

 The ethnologist expects and gains but little by examining a member of a 

 tribe hundreds of miles from his habitat and his people, but makes his 

 profitable studies of the groups of human animals in all of their undisturbed 

 relationships with their environment. The biologist must follow him in this 

 if he expects to make material progress in interpreting habit and in formu- 

 lating conceptions of adjustment by morphological differentiation, physio- 

 logical specialization, and acquisition of habital peculiarities. 



The present occasion may be profitably devoted to the consideration of 

 work with specializations displayed by existing types. After some search 

 for opportunities of promise, attention was directed toward a study of 

 dependent nutrition among seed-plants. The few observations which had 

 been made as to incidental or adventitious parasitism, in which the roots 

 of ordinarily autophytic green plants fastened on the underground mem- 

 bers of other plants, the investigations of Cannon, in which the parasitism 

 of Kramer ia upon various species was discovered, and the experiments of 

 Peirce in artificial parasitism have led to the selection. It is known that 

 organic matter may enter the absorbing organs of nearly all plants and 

 that many of the unions of two species made in grafting operations result 

 in parasitism for the cion, especially when the cion and stock represent 

 widely divergent morphological types. All of these facts show that the 

 tendency to parasitism is very strong among plants, and that a movement 

 towards its accomplishment might be made which would carry a species 

 rapidly through a wide range of adjustment. 



That this movement has affected a notable share of the higher plants is 

 evidenced by the fact that parasitism is widely prevalent in nine great fami- 

 lies or orders, and the discovery of Cannon adds to this a tenth, the Krame- 

 riaceae. One genus in every 200 includes parasites, and most impressive 

 of all is that about 2,500 species of parasitic seed-plants are known about 

 2 per cent of the recognized forms and a thorough examination would 

 doubtless double this number. A much wider category of plants is 



