ACTION OF THE NERVOUS SYSTEM. 73 



" I will remark beforehand that I pass over here 

 a line of phenomena of after-effects which may be 

 observed in the vegetable kingdom ; so, for example, 

 the after-effects displayed in bending upward from 

 the earth, and in the inclining toward the light. 

 When a shoot that has been placed in a horizontal 

 position for a while, still continues its bending 

 growth after it has been changed to a vertical 

 position, we see a simple case of after-effect ; also 

 when leaves that have grown in darkness and then 

 have been illuminated for a short time, still continue 

 to grow toward the temporary source of light after 

 it has been removed, we see another simple case 

 of after-effect. Both of these cases may be ac- 

 counted for by saying that those movements of the 

 plants which are produced by external influences, 

 do not immediately cease at the instant when the 

 external influences are withdrawn, but continue for 

 a certain time afterwards. Other after-effects are 

 of a much more complicated nature. They may, of 

 course, be placed in relation to those mentioned, by 

 intermediate connecting links. 



" Let the whole top be cut off of vigorous speci- 

 mens of Helianthus, Ricinus, Cucurbita, etc., which 

 have previously developed for a long time under 

 normal conditions ; then let a glass tube be fast- 

 ened over the cut end of the stump, and the whole 



