756 



SCIENCE 



[N. S. Vol. XXVI. No. 674 



Under the assumption that organisms re- 

 spond to or react upon variations of the en- 

 vironment, we see that a difference in the char- 

 acter of the reaction of the organism should 

 be observed. 



If an organic form responds to fluctuating 

 variations of the environment, this response 

 should also be of a fluctuating character. 

 Considering the vast variety of environmental 

 conditions, such responses to fluctuating varia- 

 tion should be very frequent, indeed, should be 

 the rule, and this serves to explain the fact 

 of the "natural diversity of individuals," 

 which, according to this theory, is to be re- 

 garded as the consequence of the different re- 

 actions of individuals to fluctuating variation 

 of environment, while they grow up. These 

 reactions, however, can not be permanent, 

 either with the individual, or with the species, 

 for the individual, as well as the species, may 

 come and will come, subsequently, under the 

 opposite influence, and thus the flrst reaction 

 will be paralyzed by another one. This kind 

 of organic variation is well known, recently it 

 has been called (by de Vries) "fluctuating 

 variation," and it is the typical "variation," 

 as understood by Darwin. This variation is 

 not very apt to be transmitted by inheritance, 

 chiefly by reason of the fact that its cause is 

 not a permanent one : even if there should be a 

 tendency toward hereditary transmission, this 

 tendency is counterbalanced by the "fluctua- 

 ting" character of its cause. 



If, however, the environment begins to 

 change in a definite direction, it necessarily 

 must produce in the organisms a tendency to 

 react again and again in the same way upon 

 the changed environment. Thus we obtain a 

 condition which has been called by C. H. 

 Merriam/' pressure of environment." If or- 

 ganisms react at all upon external influences, 

 the change of the environment in a certain 

 direction must act as a pressure upon them, 

 compelling them also to show a definite direc- 

 tion in their variation. Thus we are to ex- 

 pect " definite variation," which indeed is 

 known among organic beings under different 

 names, for instance, " orthogenesis " (Eimer) 



or "mutation" (v. Waagen),* and if there 

 is any possibility that the reaction upon an 

 external stimulus may become transmissible 

 to the offspring, this should happen under such 

 conditions, the tendency to transmit acquired 

 characters being not counterbalanced any more 

 by the opposite direction in the variation of 

 the environment, but, on the contrary, being 

 favored and emphasized. In this way, I be- 

 lieve, " mutation " of species (their transfor- 

 mation) is rendered possible, namely, by the 

 pressure of permanently changed environ- 

 mental conditions, or by " mutation of en- 

 vironment." 



It is interesting to note that the above con- 

 siderations lead us to assume the existence of 

 two kinds of organic variation. First, a 

 " fluctuating variation," which is not trans- 

 mitted. I deliberately do not say trans- 

 missible, for it may be transmissible; all we 

 can safely say is, it is not transmitted. The 

 second kind of organic variation is trans- 

 mitted : it has the quality, or the tendency, to 

 " breed true," thus changing an existing 

 species in its totality into another one. This 

 process is identical with v. Waagen's " muta- 

 tion." However, there can not be a sharp dis- 

 tinguishing line between fluctuation and muta- 

 tion, and these two forms of variation should 

 run into each other, any fluctuation being 

 capable of being transformed into a true 

 breeding mutation, as soon as its cause be- 

 comes permanent : that is to say, as soon as the 

 environmental conditions, to which it is a re- 

 action, are made permanent, so that they can 

 bring to bear their influence upon each genera- 

 tion. 



A. E. Ortmann 



Carnegie Museum, 



PiTTSBUKG, Pa. 



* Here we see why I selected above the term 

 " mutation " for definite changes of environment, 

 namely, to mark the correlation to organic " mu- 

 tation." This is by no means the " mutation " 

 of de Vries, a term which should be abandoned, 

 being preoccupied on the one hand, and ill defined, 

 in fact ill conceived, on the other. See my articles 

 in Science, May 11, 1906, p. 746; June 22, 1906, 

 p. 947; August 17, 1906, p. 214; February 1, 1907, 

 p. 185. 



