TRANSMISSION OF ACQUIRED CHARACTERS. 391 



accustomed to the usual botanical views, and is more conversant 

 with other classes of biological knowledge, to consider the facts 

 brought to light by modern botany, from a general point of view. 

 Of course I shall not attempt to question the validity of the obser- 

 vations, nor even the accuracy with which the facts have been 

 interpreted. I shall only deal with the conclusions which may be 

 drawn from the facts, and I do not think that it is absolutely 

 necessary that such criticism should be made by a botanist. 

 Questions of general biological significance such as that of heredity 

 cannot be entirely solved within the single domain of either 

 zoological or botanical facts. Both botanists and zoologists must 

 give due weight to the facts of the province which is not their 

 own, and must see whether the views which they have chiefly 

 gained in the one province can be applied to the other, or whether 

 phenomena occur in the latter which are in opposition to their 

 previously formed views and which cause them to be abandoned 

 or modified. 



Detmer begins by bringing forward certain facts which prove, as 

 he believes, that rather important changes in the organism can be 

 directly produced by external influences. He is of opinion that I 

 under-estimate the weight of these influences, and that I make light 

 of the changes which may thus arise in a single individual life. 

 But obviously, it is of no importance for the question of the trans- 

 mission of acquired characters, whether the changes directly pro- 

 duced by external influences upon the soma of an individual are 

 greater or smaller : the only question is whether they can be 

 transmitted. If they can be transmitted, the smallest changes 

 might be increased by summation in the course of generations, 

 into characters of the highest degree of importance. It is in this 

 way that Lamarck and Darwin have supposed that an organism is 

 transformed by external influences. It is therefore interesting to 

 see what Detmer considers to be a, change which has been directly 

 effected. We can in this way gain a very distinct appreciation of 

 the difference in views which is caused by the different spheres of 

 experience which belong to botany and zoology. It will be useful 

 to gain a clear idea of the differences which are thus caused. 



Detmer first alludes to the dorso- ventral structure of the shoots 

 of Thuja occidental, chiefly shown in the fact that the upper 

 sides of these shoots contain the green palisade cells, while the 



