324 Report S.A.A. AovANCEMENr of Science. 



lifetime of an individual organism can he expected to make an im 

 pression on the germ-cells so deep and lasting as to manifest itself 

 in a corresponding modification of the soma of the next generation. 

 It probably takes very many generations of cumulative action to 

 bring about such a result in ordinary cases, and the exceptional cases 

 of immeciiate inheritance of conspicuous acquired characters must 

 owe their origin to exceptional conditions of which we know nothing. 

 If, however, the above quoted case is not an example of the trans- 

 mission of a tnie " Somatogenic " or acquired character, it appears 

 to me that such characters can have no existence at all, and that the 

 whole argument is futile. 



There is. also, another way of approaching the j)roblem in addi- 

 tion to that of direct evidence. Weismanns primar) difficulty, 

 which led him to deny the transmission of acquired characters, ap 

 pears to have been the difficulty of explaining the modus operandi 

 of such transmission ; if this difficulty can be overcome an important 

 step will have been taken towards the .solution of the problem. 



It may be assumed that those who den\ the inheritance of 

 acquired characters mean that the characters in question will not 

 appear in a .second generation unless the stimulus which first evoked 

 them is still operating, when, of course, the same effects mav again 

 be produced by the same causes. It is not difficult to demonstrate. 

 however, that the environment mav make a lasting impression uj)on 

 the individual organism, which mav continue to shew itself after the 

 evoking stimulus has ceased to act. 



Now. if we can thus shew that the living organism can not only 

 respond immediately to the stimulus of changed enviroimient, but 

 can — if f)ne may use the expression — store up such stimuli and be 

 influenced bv them long after the changed environment has ceased 

 to operate directly, then it appears to me, we shall have good grounds 

 for believing at any rate in the possibilitv of the inheritance of 

 acquired characters. 



As a matter of fact we have definite proof — in the existence of 

 what are known as " after-effects '" both in plants and animals — of 

 the capacity of the individual organism for storing u]) stimuli which 

 may subsequently produce a definite response. 



The well-known daily i)eriodicity of plant growth affords an 

 illustration. The light of the sun acts as a check upon the rate of 

 growth of ordinary plants, and it is easy to shew experimentally that 

 in consequence of this action the normal plant grows most rapidly 

 in the early hours of the morning after a prolonged exjxjsure to 

 darkness, antf most slowly in the afternoon, after a long exposure 

 U) daylight, ft has been .shewn that this daily periodicitv or varia- 

 tion in rate of growth in correspondence with the periodic variation 

 in environment is continued when the plant is kept in perpetual <lark- 

 ness and the direct action of changing environment therel)v rendered 

 impossible. 



A beautiful example of a similar phenomenon from ih'- animal 

 kingdom has been described bv Dr. Gamble and Mr. Keeble 



