HOW PLANTS GROW 345 



The roots of a plant take up soil water by osmosis 

 and it flows up through the stem, through the petiole of 

 the leaf, and through the veins into the palisade layer. 

 The air is composed of about .04 per cent of carbon di- 

 oxide (CO 2 ). This carbon dioxide passes through the 

 stomata into the leaf, where it and the soil water are 

 used as the raw materials for the manufacture of starch. 

 The energy necessary for this manufacturing process 

 comes from the sun in the form of heat and light. Rapid 

 starch making by leaves requires a moderate temperature 

 and abundant sunlight. Each cell of the leaf between 

 the lower and upper epidermis is full of green-colored 

 bodies called chlorophyll bodies. These give the green 

 color to the entire leaf. The chlorophyll bodies are 

 formed in the leaf when it is exposed to sunlight. When 

 a leaf is shaded, the chlorophyll disappears and the leaf 

 turns white or yellow. This can be seen by lifting a 

 board that has lain for some time on grass, by growing 

 some plants in the dark, or by noticing the yellow leaves 

 on the under part of a tree that produces a dense shade. 



These chlorophyll bodies in the presence of sunlight 

 make starch by combining water (H 2 0) with carbon 

 dioxide (C0 2 ): 6C0 2 + sH 2 = C 6 Hi 5 + i2<3. 



This starch, made during the day, must be changed 

 to sugar, a soluble substance, before it can be moved 

 from the leaf down the stem of the plant, where it is 

 stored in the form of starch (the sugar having been changed 

 back to starch), or it is joined with other elements in the 

 soil water and then used for growth, or it is stored in 

 ripening fruits in the form of protein, or the sugar may 

 be changed to fat or oils and stored in the fruit. Name 

 some fruits or seeds that contain starch, or proteins, or 

 oils. What commercial oils come from fruits or seeds? 



