Leaves. 87 



reaches the leaf has not been transmitted through it, but 

 has been arrested within it and transformed into some 

 other form of energy. This has, in fact, taken place 

 within the chloroplasts, which were seen in Observation 89. 

 It is the green substance, the chlorophyll, which has en- 

 abled the chloroplasts to accomplish this. (See Fig. 36.) 



65. Starch the First Visible Food Product. We have 

 seen by Observation 89 that starch is formed within the 

 chloroplasts, and we must conclude that the water from 

 the soil and the carbon dioxide of the atmosphere are 

 broughtHogether in them, and that the chloroplasts, em- 

 ploying the energy of the sunlight, transform these sub- 

 stances into the finished food product in the form of starch. 

 We know that starch contains exactly the chemical ele- 

 ments furnished by water and carbon dioxide, and that 

 hydrogen and oxygen exist in the same ratio in starch as 

 in water. The chemical formula for starch is C 6 H 10 O 5 , 

 while that of water is H 2 O, and of carbon dioxide CO 2 . 

 The combination of water and carbon dioxide into starch 

 might be expressed theoretically in the following formula: 

 5 H 2 O + 6 CO 2 = C 6 H 10 O 5 + 6 O 2 ; the oxygen being given 

 off to the air again through the stomata. Doubtless the 

 process is not as direct and simple as this (it is not definitely 

 known what the steps in the process are), but the equation 

 shows what excellent raw materials water and carbon diox- 

 ide are for the production of starch. 



66. The Chloroplasts. The chloroplasts (see Observation 

 89) are parts of the protoplast and are, of course, alive. 

 It is their special function to arrest the energy of the sun- 

 light, by means of the chlorophyll which they contain, 

 and employ it in the manufacture of plant food from the 

 raw materials, carbon dioxide and water. If Observations 

 89 and 92 are carefully made, it will be seen that the 



