VII.] TRANS3nSSI0N OF ACQUIRED CHARACTERS. 413 



arisen by the operation of natural selection upon the general 

 variability of plant organization. 



Simple as these conclusions are, I have failed to meet with 

 them in any of the writings of botanists, and they may perhaps 

 be of use in helping to shake the vaguely-felt opinion that the 

 characters of plants are to be chiefly referred to the direct 

 action of external influences. 



At all events it cannot be maintained that the phenomena of 

 anisotropism support the opinion mentioned above ; and the 

 mere assertion that it is highly probable that hereditary 

 characters arise as the result of external influences, is no more 

 than the expression of an unfounded individual opinion. It is 

 remarkable that Detmer should make such an assertion as the 

 outcome of his discussion of the reversed Thuja-shoot, etc., for 

 even if we admit that the dorso-ventral structure of the shoot is 

 — as Detmer believes— the direct and primary effect of the 

 action of light, the experiment with the reversed shoot would 

 prove that no part of this effect has become hereditary. 

 Although the upper side of the shoot has produced the palisade 

 parenchyma under the influence of hght for thousands of 

 generations, there is nevertheless no tendency towards the 

 establishment of any hereditary effect, for as soon as the upper 

 side of the growing shoot is artificially transformed into the 

 under side, its normal structure is at once abandoned. Hence 

 so far from lending any support to the assumption that acquired 

 characters can be transmitted, Detmer's experiment rather 

 tends to disprove this opinion. 



I think I have sufficiently shown that Detmer's reproach — 

 that I have under-estimated the effects of external influences 

 upon an organism — may be fairly directed against its author. 

 If we can believe that every structural arrangement in plants, 

 which depends upon certain external conditions, has been 

 produced in a phyletic sense by these latter, it becomes very 

 easy to explain the transformation of species ; but in accepting 

 such an explanation we are building without any foundation, 

 for the proof that acquired characters can be transmitted has 

 yet to be given. 



As a further disproof of my views Detmer quotes the so- 

 called phenomena of correlation in plants, and he believes that 

 these instances help us to conceive how the acquired changes of 



