EFFECTS OF GROWTH AS SEEN IN MOVEMENTS OF PLANT-ORGANS. 17 



Of course there are many more cases of special character, but the 

 reader is referred to Darwin's two books, Climbing Plants and the Move- 

 ments of Plants, which supply an abundance of information. 



In conclusion, I would summarize what appear to be important pro- 

 cedures in Nature. 



1. The external stimulus is the cause (by means of the responsive 

 power of the organism) of a definite or special structure in adaptation to 

 it ; e.g. light and shade causing polarity. 



2. If the direction of the stimulus be changed, the organ may move 

 so as to put itself in adjustment with it ; e.g. Phototropism, Hydro- 

 tropism, &c. 



3. The tendency only, to produce the structure may be hereditary ; e.g. 

 in the formation of adhesive pads in Ampelopsis hederacea. 



4. The structure itself may be hereditary and be more or less completely 

 formed before the influence can act ; e.g. in the formation of adhesive 

 pads in A. Veitchii. Such is the inheritance of acquired characters. 



5. The direction of the growth of the organ can be hereditary apart 

 from the presence of the original stimulus which caused it ; e.g. the 

 erection of shoots laid horizontally (originally due to light) in total 

 darkness. 



VOL. xxxv. 



c 



