THE ASSIMILATION OF PLANT FOOD 73 



excretions due to the slow passage of the denser liquid 

 from the plant take place through the root hairs, but this 

 is very small considering the amount taken in, the greater 

 quantity going to the side of the stronger solution, i.e., 

 into the plant. The solution containing the plant food 

 finds its way through the stems of the plant to the leaves; 

 there it comes into the " laboratory " of the plant, and 

 in contact with the elements derived from the atmosphere. 



60. Function of the Leaves of Plants. The water 

 which serves as the carrier of plant food from the soil 

 originally comes from the atmosphere in the form of rain 

 water. Carbon diox'.de comes from the atmosphere, and 

 is taken into the plant through small openings in the leaf, 

 known as the stomata. The stomata form the breathing 

 pores of the plants. Through them carbon dioxide is taken 

 into the plant and oxygen is given off. In the leaves of 

 the plant, all of the various elements of plant food are 

 brought together and are built up into the proximate con- 

 stituents of the plant. This process is termed photosyn- 

 thesis. Photosynthesis takes place only in plants which 

 contain green coloring matter. The material that produces 

 the green coloring of plants is known as chlorophyl. 



The simplest photosynthesis is that in which formalde- 

 hyde is produced. This is made into carbohydrates. The 

 process is accomplished in the leaves of the plants under 

 the influence of chlorophyl, sunlight, and aqueous carbon 

 dioxide. It may be expressed in chemical equation : 



CO 2 +H 2 O = CH 2 O+O 2 , 



Carbon dioxide and water yield formic aldehyde (CH 2 0) 

 and oxygen. The oxygen given off serves to replenish 

 the atmosphere and aids in maintaining the balance be- 

 tween plant and animal life. Six molecules of formic 

 aldehyde, by condensation, form sugar (CeH^Oe). The 

 sugars are soluble, and it is in this form that the carbo- 



