The Anatomy and Physiology of Plants 67 



the interior of the leaf.. These cells are full of the green 

 chlorophyll granules. The air, as we have seen, always 

 contains a minute portion of carbon dioxide or carbonic 

 acid gas. When the sun shines, and at no other time, the 

 mouths of the leaf, or the stomata (singular stoma), open, 

 and the air with the carbon dioxide, can penetrate to the 

 interior of the leaf, there coming in contact with the green 

 granules. This green material has the extraordinary 

 power of breaking up the combination of the carbon and 

 oxygen in the carbon dioxide and taking in the carbon. 

 The leaf throws off the oxygen and thus serves to purify 

 the air from the carbon dioxide which, while furnishing 

 food to the plant, is poisonous to animal Hfe. It cannot 

 of course be determined that the plant does throw off the 

 identical oxygen that was combined with the carbon, but 

 it does throw off about the same amount. Getting this 

 carbon, then, from the air, the Uving matter in the cells of 

 the leaf goes to work to make further combinations with 

 it and the hydrogen, oxygen, and other matters brought 

 from the soil. So it constructs new material for new cell 

 walls, for renewing the waste of Hving matter, and for the 

 purposes of growth in general. 



The materials elaborated in the leaves are sent to every 

 part of the plant where cells are forming and growth is 

 going on. To the remotest tip of the shoots and the 

 farthest rootlet, the materials for growth are sent from 

 the leaves, so that whatever the leaf of a plant is that will 

 be what the plant as a whole is. No mistake is ever made. 

 The leaves of the apple tree manufacture material for 

 apple wood, apple roots, and apple leaves only. The oak 

 and the pine growing side by side with their roots inter- 



