750 THE AMERICAN NATURALIST. (Vor. XXXIX. 
elementary species appear suddenly, without intermediate steps. 
New forms spring laterally from the main stem. New elementary 
species attain their full constancy at once. Some new strains are 
evidently elementary species, while others are to be considered as 
varieties. The same new species are produced in a large number 
of individuals. The mutations take place in nearly all directions. 
The great difference between this and the Darwinian theory of the 
origin of species is that here we have new forms which are to be 
recognized as specifically distinct, arising in perfectly constant form, 
by sudden leaps, or more properly mutations, rather than by contin- 
uous slow variations. This and the fact that many individuals, whole 
species indeed, are mutating simultaneously, must profoundly modify 
the Darwinian concept. It is superfluous here to enter further into 
this discussion or to point out how in other ways our ideas must be 
rearranged to be consonant with these new facts. That the question 
is completely solved no one, probably the author least of all, would 
be prepared to admit, but that much light has been thrown on the 
matter can hardly be questioned. It has been said somewhere that 
while Professor de Vries has given us a Mutation Theory he has not 
given us a Theory of Mutation. That may indeed be true, but let 
us at least be thankful that here we have this question of the origin 
of species at last within the field of experimentation. Perhaps it 
will be possible for us to determine later what are the predisposing 
conditions or influences which make for mutation, whether or not 
there is any definite periodicity to the phenomenon. Not least im- 
portant, too, is the bringing of the whole matter within the scope of 
physiological inquiry, and the insistence that morphological tests un- 
confirmed by physiological ones are only provisional. There is 
bound, of course, to be considerable misconception as to what really 
are and what are not mutations, and the intuitive plant-breeder will 
no doubt be tempted to lay too great confidence on the scientific 
value of his own experiments, yet in this way too the book, if under- 
standingly read, will prove of the greatest value. It cannot be too 
often stated that the confidence one has in the results of Professor 
de Vries is that his were pedigree cultures guarded from contamina- 
tion with the greatest care and with the complete ancestry of his 
plants minately recorded from the time he undertook the work. 
Bienen T no see for any scientific investigator pro- 
odio 1 er Im o research in a loose or careless way after 
Ser re S yet it ought to, and no doubt will, stimulate 
0, themselves, add something to the sum of 
