10 METHODS OF EVOLUTION [CHAP. 



pads formed on the tips of the thread-like 

 tendrils of the American Virginia creeper 

 (Ampelopsis hederacea] are never formed until 

 contact with a wall or rock, etc., has taken place. 

 They result from the irritation ; but they are 

 not hereditary. It is only the power to make 

 them which is hereditary. 



On the other hand, in the Japanese species 

 (A. Veitchii? fig. 1) they are already formed, 

 but only partially developed before any contact 

 at all. In this species, therefore, they are 

 hereditary, but quite useless until contact has 

 taken place ; when they at once begin to 

 develop into perfectly adaptive structures. Such 

 is obviously a result of a Response with Adapta- 

 tion to a purely mechanical contact of the soma 

 with the wall, and before any reproductive 

 germ-cells exist. There are many other cases 

 of permanent and hereditary results of the 

 influence of simply physical forces, such as 

 pressure, weight, etc. These are quite sufficient 

 to call out a responsive action by which, some- 

 times temporary, at others hereditary, results 

 accrue. 



Moreover, these effects are altogether con- 

 nected with the soma or vegetative system, long 

 before any reproductive organs exist ; yet, when 

 these put in an appearance, the seeds have some- 



1 Similar " pads " are hereditary in Bignonia kaplophyllum and 

 Arthrophyttum cirrhatum. 



