152 PLANT RELATIONS. 



an active stem be cut and plunged into water stained with 

 an aniline color called eosin,* the ascending water will stain 

 its pathway. After some time sections through the stem 

 will show that the water has traveled upwards through it, 

 and the stain will point out the region of the stem used in 

 the movement. 



In general, therefore, the carbon dioxide is absorbed 

 directly from the air by the leaves, and the water is ab- 

 sorbed by the root from the soil, and moves upwards through 

 the stem into the leaves. An interesting fact about these 

 raw materials is that they are very common waste products. 

 They are waste products because in most life-processes they 

 cannot be taken to pieces and used. The fact that they 



can be used in photosynthesis 

 shows that it is a very re- 

 markable life process. 



(2) Cliloroplasts. — Having 

 obtained some knowledge of 

 the raw materials used in 

 photosynthesis, and their 



Fig. 145. Some mesophyll cells from A J 



the leaf of Fittonia, showing chloro- SOUrceS, it IS necessary to 



P laBts - consider the plant machinery 



arranged for the work. In the working leaf cells it is 

 discovered that the color is due to the presence of very 

 small green bodies, known as chlorophyll bodies or cliloro- 

 plasts (see Fig. 145). These consist of the living substance, 

 known as protoplasm, and the green stain called chloro- 

 phyll ; therefore, each chloroplast is a living body (plastid) 

 stained green. It is in these cliloroplasts that the work of 

 photosynthesis is done. In order that they may work it 

 is necessary for them to obtain a supply of energy from 

 some outside source, and the source used in nature is sun- 

 light. The green stain (chlorophyll) seems to be used in 

 absorbing the necessary energy from sunlight, and the 



* The commoner grades of red ink are usually solutions of eosin. 



