122 



The Plant World 



begun by Darwin has been most forcefully completed bv De 

 Vries. Like Darwin, his well considered results obtained by 

 twenty years of experimental cultures have been brought out 

 with a new theory for the interpretation of certain phases of 

 evolutionary development. Without appraisement of the im- 

 portance of mutation as a factor in evolutionary procedure, 

 it is to be said that the greater service performed by DeVries 

 consisted in his demonstration that the method of trial and test 

 is one by which major phenomena in heredity may be appre- 

 hended, their course, frequency and scope measured, and by 

 operations of so simple a nature that it has enormously stimulated 

 research upon the subjects concerned. The power of investi- 

 gating at first hand many of the activities of organisms upon 

 which rest some of the most essential features of descent, has 

 thus been placed in the possession of a great biological con- 

 stituency. The resultant specialization of effort made possible 

 with the consensus of thinking upon the general principles in- 

 volved which may follow, is an ideal condition from which 

 substantial advance may be expected. 



It is notable that with the revivification of any branch 

 of biology by the subjection of its materials and conclusions to 

 methods of control and measurement constituting experimenta- 

 tion, a tendency is exhibited by its representatives to illustrate 

 the change by its terminology. Sachs' first book bore the 

 German equivalent of "Handbook of Experimental Plant 

 Physiology"; works on morphology are similarly designated to 

 distinguish them from treatises on comparative anatomy mas- 

 querading under the larger title, although physiology has pro- 

 gressed so far as to drop the adjective, in tacit and full acknowl- 

 edgement that no course of reasoning upon functionation or 

 ontogenetic procedure has any claim to be denoted as physiology 

 which is not grounded upon experimental evidence. My corres- 

 spondence files show that DeVries wished to use the term 

 "experimental" to indicate that his work upon mutations as 

 described in "Species and Varieties" was based upon trials and 

 tests in cultures rather than disconnected observations, while 

 a department of the Carnegie Institution still finds it useful to 

 define the aspects and mode of treatment of evolution to which 

 its resources are devoted. 



