Characters, Hereditary and Acquired. 129 



of heredity would expect. Indeed, looking to the 

 known potency of reversion, the wonder is that in any 

 case such changes should become hereditary in a single 

 generation. On the other hand, there is no reason to 

 imagine that the hypothetical germ-plasm — howsoever 

 unstable we may suppose it to be — can admit of being 

 directly affected by a change of soil in a single 

 generation. For, on this view, it must presumably be 

 chiefly affected during the short time that the seed is 

 germinating ; and during that time the changed con- 

 ditions can scarcely be conceived as having any points 

 of attack, so to speak, upon the residual germ-plasm. 

 There arc no roots on which the change of soil can 

 make itself perceptible, nor any stem and leaves on 

 which the change of atmosphere can operate. Yet the 

 changed conditions may produce hereditary modifica- 

 tions in any parts of the plant, which are not only 

 precisely analogous to non-hereditary changes similarly 

 produced in the somatic tissues of innumerable other 

 plants, but are always of precisely the same kind in 

 the same lot of plants that are aft'ected. When all the 

 radishes grown from wild seed in Paris, for instance, 

 varied in the direction of rotundity and dark colour, 

 while those grown in the country presented the opposite 

 characters, we can well understand the facts as due 

 to an entire season's action upon the whole of the 

 growing plant, with the result that all the changes 

 produced in each set of plants were similar — just as 

 in the cases where similarly ' climatic " modifications 

 are not hereditary, and therefore unquestionably due 

 to changed conditions acting on roots, stems, leaves, 

 or flowers, as the case may be. On the other hand, 

 it is not thus intelligible that during the short 

 II. K 



