CHLOROPHYLL 75 



forms only about three -hundredths of 1 per cent of the air. 

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

 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 com- 

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

 means that carbon dioxid has drained into the place. The 

 air of a closed school -room 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. 



158. APPROPRIATION OF THE CARBON. The carbon di- 

 oxid of the air readily diffuses into the leaves and other 

 green parts of the plant. The leaf is delicate in texture, 

 and often the air can enter directly into the leaf tissues. 

 There are, however, special inlets provided for the admis- 

 sion 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. The apple leaf contains about one hundred 

 thousand of these pores to each square inch of the under 

 surface. Through these breathing pores the outside air 

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

 little cells containing the living matter. In Part III these 

 breathing pores will be studied. 



159. CHLOROPHYLL. The green color of leaves is due to 

 a substance called chlorophyll. Purchase at the drug store 

 about a gill of wood alcohol. Secure a leaf of geranium, 

 clover, or other plant which has been exposed to sun- 

 light 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, 



