THE AMERICAN BOTANIST 111 



1 Irlintropisiii prevails xi c.\tcii>i\ c'l\' aiiionj;' the higher 

 |)laiit> that there are extremely tew of which some part does 

 not hem! towards a lateral light. The insectivorous [)lants 

 are exceptions to thisjtor it is ohxious that thev do not live 

 ohieHx' 1)\- deconii)()sing carhonic acid, hut it is of more impor- 

 tance to them that their leaves should occupy the hest position 

 for cai)turing insects. Also the stems of twining plants are 

 rarely heliotroi)ic for if they had a tendenc\- to move towards 

 a lateral light, they would he dr.iwn away from their supports. 

 Most tendrils are apheliotropic and thus find supports. 



Paraheliotropism has undouhtedly been accjuired for a 

 definite purpose. The chlorophyl of leaves is liable to become 

 injured from too much light, and it is believed that it is pro- 

 tected bv the jnost tliversihetl means, such as the pre.sence 

 of hair>, coloring matter, and amongst other means, by the 

 leaves presenting their edges to the sun so that the blades re- 

 ceive the smallest amount of light. It is very probable that 

 thi.s nio\ement has been acquired for the si)ecial purpose of 

 avoiding too intense illumination. 



It is of paramount importance to the chlorophyl man- 

 ufacture that the leaves get all the sunlight possible. As it 

 falls on the sensitive protoplasm of the plant, the light sets 

 u[), probablv bv chemical means, a condition of initation or 

 strain which puts the side toward the light in a condition dif- 

 ferent from the side away from it. thus favoring the chloro- 

 ph)l process. This is well shown I)y the plants growing on 

 a bank or on the borders of a wood. The trees send their 

 greater number of branches) towards the open, and in the ca.se 

 of plants growing on a bank, the leaves are so mosaicked 

 that they are not one on top of the other, but each is so ar- 

 ranged that the greater area is presented to the sun. Some 

 botanists have advocated the idea that the angular shape of 



