i8 



Nature- Study Agriculture 



What 

 plants 

 secure from 

 carbon 

 dioxid 



Why 



motion of 

 the air is 

 necessary 



several days or weeks, it dies as surely as does an animal 

 that is deprived of air. (Exp. 9.) Though plants 

 absorb oxygen over their entire surfaces, they obtain 

 the greater part of their supply through the leaves and 

 roots. Sometimes, in a city or village, the leaves of a 

 beautiful, healthy-appearing shade tree suddenly begin 

 to wither and the tree dies. This is usually caused by 

 gas escaping from the mains. The gas fills the air spaces 

 in the soil, drives out the soil air, and the tree is suffo- 

 cated. 



Carbon dioxid. Though oxygen is essential, it is 

 not required in nearly such quantity for the manufacture 

 of foods as is carbon dioxid. (Exp. 10.) Carbon 

 dioxid gas is the -material from which plants secure the 

 carbon that enters into the making of carbohydrates 

 (starch, sugar, woody fiber, etc.). Carbon dioxid is 

 also essential in the manufacture of the proteins and oils 

 found in plants. Proteins and oils are for the most part 

 formed within the seeds, as protein in beans, and oil 

 in cottonseed, linseed, and olives. (Carbon dioxid is 

 often spoken of as " carbonic acid gas," and the chemists 

 abbreviate the name by writing it CO 2 , the characters 

 indicating that the gas is composed of one part carbon 

 and two parts oxygen.) 



There is so little carbon dioxid that in ten thousand 

 parts of air only about three parts consist of this gas. 

 Nevertheless, plants feed upon it so hungrily that they 

 succeed in absorbing immense quantities of it. If the 

 air were perfectly still, plants could not get sufficient 

 carbon dioxid. For example, a three-hundred-bushel 

 crop of potatoes on an acre uses as much of this gas as 



