Januaby 24, 1908] 



SCIENCE 



127 



similar to that which oeeui*s in bud-sports 

 or vegetative mutations, about which but 

 little is known. 



The opportunity does not permit an 

 extended and thorough comparison be- 

 tween the results obtained by Tower with 

 beetles and those by myself with plants, 

 but the following points may be noted: 

 The experimentally produced derivatives 

 of beetles diverged from the parental type 

 principally by one main character, with 

 correlated variability in others. The in- 

 duced forms in plants show many new 

 qualities of fairly equal importance, so far 

 as such things may be estimated, and these 

 might be quite independent of each other. 

 The new forms of beetles crossed readily 

 and were readily swaxaped by the parental 

 or other types. The new plants do not 

 hybridize freely, if at all, even when grown 

 with branches interlocking with the pa- 

 rental type. The few tests with the deriva- 

 tives of Raimannia in New York and at 

 the Desert Laboratory show it to be less 

 capable of endurance to these climates, both 

 of which are foreign to the parental type, 

 than the parent. The derivatives of (Eno- 

 thera hiennis show equal endurance with 

 the parent in the native habitat, and at the 

 Desert Laboratory (2,700 ft.), but exceed 

 it at the montane station (8,000 ft.). The 

 changes produced in beetles are supposed 

 to be a purely stimulative effect in the 

 growth or maturation period of the egg, 

 while those of plants may be due to similar 

 action, or to the direct chemical disturb- 

 ances produced by the reagents, during the 

 period following the reducing division. 



A restatement of the principal protheses 

 of the work in hand upon the relation be- 

 tween environic and other factors and 

 heredity will be profitable in closing. 

 These may be briefly given as follows: 



The forms and qualities exhibited by 

 organisms represent the total effect of en- 

 vironment, but it can not be shown that 



this has been brought about by direct 

 adaptation; many of the most highly spe- 

 cialized and useful structures bear only an 

 indirect relation to the factors to which 

 they bear a useful relation. Neither has 

 it been demonstrated that an individual ad- 

 justment made by the soma is impressed 

 upon the germ-plasm, and transmitted un- 

 changed, although the inference is strong 

 that this may be involved in rhytlunical 

 functions and perhaps in range of vari- 

 ability. 



Various agencies experimentally applied 

 in such manner as to affect the germ-plasm 

 only have caused the origin of forms bear- 

 ing fully transmissible qualities not pre- 

 sented by the parental type. The new 

 characters have been found to be fully 

 heritable, and the induced forms do not 

 always hybridize with the older types. 



The induction of such new forms in 

 plants may be accomplished by reagents 

 applied to the generative nuclei carried by 

 the pollen-tube, and probably by action on 

 the embryo-sac, in the period followinp; 

 reduction division. Mutations have been 

 taken, on hypothetical grounds, to be based 

 on changes occurring previous to these 

 divisions. 



The various agencies used in inducing 

 new forms in this manner may have a 

 stimulating effect, or may caiise dir-gct dis- 

 turbances in the chemical balance of the 

 substances in the chromatin and plasma. 

 Similar action may result from unusual 

 intensities of various environmental condi- 

 tions, or to accidental intrusions on germ- 

 plasm of many kinds. The alterations in 

 question may well be beyond detection by 

 cytological, or by any direct method of 

 examination. 



When the nature of the induced changes 

 is once ascertained, the inductive agents 

 might be applied in such manner as to 

 guide the course of development and thus 

 actually control the evolution of organ- 



