136 THE PRINCIPLES OF FLORICULTURE 



more abundant on the lower side, are the guard 

 cells. They surround various openings in the 

 leaf, which are called stomata. 



(c) Palisade cells. Palisade cells are narrow, upright 



cells, placed closely together near the upper surface 

 of the leaf. They contain many chloroplasts. 



(d) Spongy cells or parenchyma. Below the palisade 



cells are located large, loose cells with many air 

 spaces between them. These air spaces usually 

 connect directly with the stomata. 



Other cells of the leaf are vascular bundles or veins, and 

 storage cells, similar to those which are found in roots. 



GROWTH AND HOW IT IS ACCOMPLISHED 



As has been stated, life, in even the higher plants, begins 

 with a single cell. This cell is the dwelling place for the 

 vital fluid which is known as protoplasm, and contains 

 the most vital of all parts, the cell nucleus. Protoplasm 

 possesses a strong affinity for water, and by a process which 

 botanists call osmosis, it draws water into itself until the 

 cell wall is fully distended. Osmosis, then, is the attrac- 

 tion which a denser liquid has for one less dense. As long 

 as the soil water is not too highly charged with food sub- 

 stances, the protoplasm draws in through the cell wall, not 

 only soil water, but also food substances which the water 

 holds in solution. This is passed on to other cells by os- 

 motic action and by the tendency of liquids to diffuse until 

 all parts are of a uniform character. Thus enriched, the 

 protoplasm begins to form a new cell wall which always 

 extends through the nucleus, dividing it so that a portion 

 goes into each new cell. Thus cell division goes on in- 

 definitely. 



