January 24, 1908] 



SCIENCE 



123 



tinuanee of the stimulus and of the re- 

 sponse results in heritable and irreversible 

 modifications, we have an idea resting 

 upon inference, and based upon supposi- 

 tions and circumstantial evidence only, 

 since no satisfactory proof has yet been 

 offered to show that a modified soma might 

 impress its divergent characters upon the 

 germ-plasm. 



It seems necessary to repeat and empha- 

 size the assertion that no case exists, in 

 which it has been demonstrated, or proved 

 beyond reasonable doubt, that any fully 

 and continuously heritable change has been 

 induced in a plant by the conditions of 

 cultivation, outside of those due to selec- 

 tion, hybridism and mutation. Individ- 

 uals may be forced to the limit of their 

 variability by culture, and the effect may 

 endure for, a few generations when the in- 

 citing causes are removed, but it finally dis- 

 appears. Thus when a species is ac- 

 climatized poleward, it shows a seasonal 

 cycle of lessened length, or instead of an- 

 nual it becomes biennial, this being a fair 

 example of a direct useful and necessary 

 adaptation and one of the clearest that can 

 be found. A return to lower latitudes is 

 followed by a reversion to the original 

 habit, however, a process which may need 

 two or more generations for its completion. 

 The movement of a species toward the 

 equator may result in a perennial habit, 

 likewise of a temporary character. 



While satisfactory proof of direct indi- 

 vidual adaptation and its heritability is 

 not at hand, and while many of the most 

 highly specialized adaptations are known 

 to have no causal connection with the ex- 

 ternal agency concerned, yet the possibili- 

 ties are not to be ignored. The very vague- 

 ness of the subject is a challenge, and it 

 is with the view to testing evidence and 

 obtaining new facts, that the Desert 

 Laboratory has established experimental 

 cultures through a range of a vertical mile, 



from subtropical arid, to alpine humid 

 climates, in which introductions and ex- 

 changes already made have been followed 

 by marked somatic alterations. It re- 

 mains to be seen whether any of these are 

 adaptive, and whether the changes in ques- 

 tion are irreversible or not. A decade will 

 be necessary for any intelligent considera- 

 tion of even the simpler phases of the 

 subject. 



It is now pertinent for us to inquire as 

 to the possible stimulative or formative ac- 

 tion which external forces may exert on 

 the germ-plasm independently of the 

 somatic or vegetative body, in the produc- 

 tion of heritable alterations. 



Experimentation upon the subject has, 

 until recently, been carried on with the 

 idea of producing somatic modifications, 

 which might by repetition, or by pro- 

 fundity of alternation, be impressed on 

 the germ-plasm and thus conveyed to suc- 

 cessive generations. Recently, however. 

 Tower has carried his work in the induc- 

 tion of new forms of beetles by climatic 

 and other factore, to a point where he is 

 satisfied that the effect of the external 

 agent is directly upon the germ-plasm, 

 with what remarkable results, as set forth 

 in his notable contribution, you are already 

 doubtless familiar. 



My own investigations bearing upon this 

 matter were successful in methods in which 

 the action of the experimental agencies 

 upon the germ-plasm was direct and 

 capable of ready demonstration. As an- 

 nounced in 1905 it was found that the in- 

 jection of various solutions into ovaries of 

 Eaimannia was followed by the production 

 of seeds bearing qualities not exhibited by 

 the parent, wholly irreversible, and fully 

 transmissible in successive generations. 



Encouraged by this success, a number of 

 reagents were used in the following year 

 with (Enothera biennis, a plant which had 

 been under observation for some time, and 



