282 GENETICS IN RELATION TO AGRICULTURE 



elementary species. De Vries, therefore, classified the "mutants" as 

 follows: 



I. Progressive species gigas, rubrinervis. 

 II. Degressive species albida, oblonga. 



III. Regressive species or) 7 .. 7 . , . ,. 



. .. } nanella, Icevifoha, bretnstyhs. 

 retrograde varieties j 



IV. Inconstant species lata, scintillans. 



These were considered the important mutations although several 

 others were recognized and given names but because of sterility or lack 

 of space and time for growing them they were not preserved. 



The Mutation Theory of Evolution. Based on the observations and 

 experiments above reviewed, de Vries formulated a set of "laws of 

 mutability" for the evening primroses which serve as an epitome of 

 his theory of evolution. Omitting further discussion of the evidence for 

 the present, the laws themselves are stated as follows : 



I. New elementary species appear suddenly without intermediate 

 steps. 



II. New forms spring laterally from the main stem. 



III. New elementary species attain their full constancy at once. 



IV. Some of the new strains are evidently elementary species, 

 while others are to be considered as varieties. 



V. The same new species may be produced in a large number of 

 individuals. 



VI. Mutability is entirely independent of fluctuating variability. 

 VII. The mutations take place in nearly all directions. To these 

 an eighth must be added in order to complete the theory: 



VIII. Natural selection eliminates all unfit mutants originating in 

 the wild. 



De Vries found many examples of the sudden origin of new forms in 

 the history of domesticated animals and plants and pointed out various 

 practical applications of his discovery, to some of which we shall have 

 occasion to refer later. For the present it is necessary to give further 

 consideration to the evidence in the case of the (Enothera "mutants" 

 and to the interpretation thereof in order to arrive at a definite conception 

 of the true nature of these aberrant forms. For this purpose it will 

 be necessary to summarize in a general way the researches which have 

 been made since de Vries' original work. 



The publication of "Die Mutationstheorie " aroused widespread 

 interest and brought forth certain criticisms concerning the biological 

 basis for de Vries' conclusions. The opponents of the theory assumed 

 (Enothera lamarckiana to be of hybrid origin and pointed out that upon 

 such a basis the so-called mutations are merely recombinations of ances- 



