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 
retrograde varieties 
IV. Inconstant species—lata, scintillans. 
—nanella, levifolia, brevistylis. 
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 Cinothera “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 
Gnothera lamarckiana to be of hybrid origin and pointed out that upon 
such a basis the so-called mutations are merely recombinations of ances- 
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