No. 529] 



ORGANIC RESPONSE 



33 



reappearance of the spines is, therefore, one of regres- 

 sion; in a paper before this society a year ago I was 

 able to present results of experimental parasitism, in 

 which the reactions of autophytic green plants when 

 grown as parasites included a number of phenomena, 

 which were not only not adaptive in any sense, but which 

 might reasonably be considered as distinctly unsuitable. 

 Among these was included the very striking autonomic 

 movements of etiolated segments of the prickly pear 

 (Opuntia) when it was led to fasten upon other plants as 

 a parasite. 20 



Many alterations in plants in the cultures, however, 

 particularly those concerning the reproductive habits, 

 may readily be interpreted as being adjustments of a 

 directly adaptive character. With these are many cor- 

 relative changes which are simply carried along. It 

 seems fairly certain that the distinction between the pri- 

 mary adjustive alterations and correlative effects will 

 be made clearer in any analyses made of the possibil- 

 ities of inheritance of somatic changes. In connec- 

 tion with the discussion of the nature of the parasitic 

 adjustments the behavior of a drop of water when rest- 

 ing upon a rough surface was offered as an illustration 

 of the modifications of an organism under environ- 

 mental influences. The sectors of the drop in direct 

 contact with a hard object which is not wetted will 

 be most markedly and directly altered, in a manner 

 parallel to the reactions in functions most directly af- 

 fected by environment, while the free sectors or qualities 

 of the drop or of the organism will be altered in various 

 degrees by correlation stresses. 



So far as the responses in the cultures at the four plan- 

 tations are concerned, they appear to the fullest extent at 

 oneeand in the first generation. Whether any of them may 

 become fixed and transmissible in a long series of genera- 

 tions subjected to the same conditions, like Daphnia, re- 

 mains to be determined. That this might be the most 



^MacDougal and Cannon, "The Conditions of Parasitism in Plants," 

 Pub. No. 29, Carnegie Institution of Washington, 1910, p. 37. 



