CARBON AND CHLOROPHYLL 83 



would be very disastrous to animal life, however, if this 

 small percentage were much increased, for it excludes the 

 life-giving oxygen. Carbon dioxid is often called "foul- 

 gas." It may accumulate in old wells, and an experienced 

 person will not descend into such wells until they have been 

 tested with a torch. If the air in the well will not support 

 combustion, that is, if the torch is extinguished, it usually 

 means that carbon dioxid has drained into the place. The 

 air of a closed schoolroom often contains far too much 

 of this gas along with little solid particles of waste matters. 

 Carbon dioxid is often known as carbonic acid gas. 



173. Appropriation of the Carbon. — The carbon dioxid 

 of the air readily diffuses into the leaves and other green 

 parts of the plant. The leaf may be delicate in texture, and 

 air may diffuse directly into the leaf-tissues. There are, how- 

 ever, special inlets adapted for the admission of gases into 

 the leaves and other green parts. These inlets consist of 

 numerous pores (stomates or stomata), which are especially 

 abundant on the under surface of the leaf. They may also 

 be present on the upper surface. The apple leaf contains 

 about one hundred thousand of these pores to each square 

 inch of the under surface. Through these pores the outside air 

 enters into the air-spaces of the plant, and finally into the 

 little cells containing the living matter. In Chapter XL 

 these stomata will be studied. 



174. Chlorophyll. — The green color of leaves is due to a 

 substance called chlorophyll. Purchase at the drug store 

 about a gill of (grain) alcohol. Secure a leaf of geranium, clover, 

 or other plant that has been exposed to sunlight for a few 

 hours and, after dipping it for a minute in boiling water, 

 put it in a white cup with sufficient alcohol to cover the 

 leaf. Place the cup on the stove where it is not hot enough 

 for the alcohol to take fire. After a time the chlorophyll is 

 dissolved by the alcohol, which has become an intense 

 green. Save this leaf for a future experiment. Without 



