42 



STRUCTURAL BOTANY 



The blade of the leaf is only two cells thick, except 

 at the midrib, where it is thicker. The cells of the 

 midrib are long and narrow, those of the rest of the 

 blade are shorter and broader. The movement 

 generally begins first in the long narrow cells. 



Fio. 19. A few cells from the leaf of the American Water- 

 weed, a, 6, c, d, e, nuclei of the various cells ;/, a strand 

 of protoplasm crossing the cell-cavity ; g, h, i, chloro- 

 phyll granules, some of which are dividing. The small 

 bodies inside the chlorophyll granules are starch. (After 

 Kny.) Magnified several hundred times. The narrow 

 cell, to the left, would show rotation ; the broader cells, to 

 the right, circulation. 



Each cell has a fairly thick layer of protoplasm 

 (primordial utricle) lining its cell-wall, and in this 

 protoplasm numerous large chlorophyll granules are 



