THE VITAL PROPERTIES OF THE CELL 



105 



investigation of Stahl (IV. 34), which he conducted on the lines 

 laid down bj Famintzin, Frank, and Borodin. When the illumina- 

 tion is faint, or when the leaves are in shadow, the protoplasm 

 moves so that the chlorophyll granules are arranged upon those 

 external surfaces of the cells which are turned towards the light 

 (Fig. 5'2^), having completely forsaken the side-walls. On the 

 other hand, the protoplasm, under the influence of direct sunlight, 

 streams away towards the side- walls, until the external surface is 

 quite free from chlorophyll granules, that is to say, in the first 



FIG. 52. Tran- verse section through the leaf of / emna trisulca (after Stahl) : A surface 

 position (position assumed in diffused sunlight) ; B arrangement of chlorophyll granules 

 under the influence of intense light ; C position assumed by chlorophyll granules in the 

 dark. 



case, the whole chlorophyll-bearing substance, as in Mesocarpus, 

 assumes a surface position towards the impinging light, and in the 

 second, a profile position ; hence the varying colour of the leaves. 



