HOW THE PLANT LIVES 



127 



194a. Air in which seeds have been germinating has suffered 

 a change; this can be shown in the following manner: Fill a 

 large-mouthed bottle half full with soaked beans or peas, add a 

 small quantity of water, and cork it. After twenty-four hours, 

 pass a lighted wax taper or waxed cord into the jar, and it will be 



extinguished. Make the same 

 tests in a jar of air, and see that 

 the taper burns. This is a striking 

 change. As a matter of fact, the 

 germination has increased the 

 amount of carbon dioxid and di- 

 minished the amount of oxygen, 



but other more elaborate experi- 

 ments would be needed to show 

 how we know that these are the 

 gases affected. 



196a. For a discussion of 

 the relation of wet soils to oxy- 

 gen-absorption, read Soraner, 

 pp. 77-80. 



196/>. The "cypress 

 knees " which project 

 from the water in cypress 

 swamps in the South are 

 supposed to be aerating 



Fig. 40. Means of showing tranapiratii 



organs. 



197a. If a plant is 



burned in tho air, the resulting ash is very small ; but if burned 

 without free access of air, as in a charcoal pit, there remains 

 a charred mass almost, as great in volume as the substance 

 burned. This mass is largely carbon, a most important element 

 in all living matter, or protoplasm. In combination with the 

 elements of water, carbon also forms most of the cellular tissue 

 of plants, likewise the starches and the sugars, all of which are 

 called carbohydrates. The manufacture of these sturch-like com- 

 pounds by the appropriation of the carbon dioxid of the air is 



