PLANT STRUCTURE 141 



depending upon the requirements of a partic- 

 ular species of plant for food-manufacturing 

 areas. The number of green plastids also varies 

 in different species, due to the amount of food 

 required by that particular species. This ex- 

 plains why leaves are of different shades of 

 green. 



(1) Spongy cells or spongy parenchyma. 

 Spongy cells or spongy parenchyma are below 

 the palisade cells. They serve to collect gases 

 and liquids and to hold them until the palisade 

 cells use them in the manufacture of food. 

 They also contain some chloroplasts and, there- 

 fore, serve to some extent in changing crude 

 food substances into usable forms. In thick 

 leaves, these cells are useful for storage of 

 reserve plant food. 



Running through the leaf tissue are numerous 

 vascular bundles which are similar in structure 

 and function to the vascular system of the stem 

 and root. These serve to transport the liquids 

 of the plant. They are called veins. 



CELL FUNCTIONS 



A plant's environment, as regards soil, moisture and 

 atmospheric conditions, has an intimate relation to the 

 ability of the plant cells to perform their normal functions. 



108. Number and function of root-hairs. As has been 

 stated, root-hairs develop in large numbers just back of 

 the root-cap, which is the section of growth and consequent 

 elongation of the root. As the tip of the root grows, 



