78 ON SAP. 



Mrs. B. The analogy is perhaps even stronger than 

 you imagine ; for this process, which in animals is perform- 

 ed by means of breathing atmospherical air, in vegetables 

 is performed by the same air acting on the sap when it 

 comes in contact with it at the stomas : the leaves may 

 therefore be considered as the lungs or organs of respi- 

 ration of plants. 



Emily. How curious ! their stomas then are so many 

 little breathing mouths. And does the oxygen of the at- 

 mospherical air carry off carbon from the sap, as it does 

 from the chyle ? 



Mrs. B. On the contrary, carbon or charcoal is the 

 principal ingredient of wood and of all vegetable matters : 

 the object to be aimed at is therefore to increase, instead 

 of to diminish, the quantity contained in the sap ; and the 

 chemical process to which this fluid is submitted in the 

 leaves, though analogous to that performed by the lungs, 

 so far as it prepares the sap for being assimilated to the 

 plant, is rather opposed to it, so far as regards its chem- 

 ical results. 



We animals, the most favored part of the creation, en- 

 dowed with the faculty of locomotion, require to be of a 

 lighter structure than our tough woody neighbors who are 

 attached to the soil ; and, in order to move about with 

 facility, it is necessary for us to disencumber ourselves of 

 part of the carbon we consume in feeding on vegetables ; 

 and a man you know, exhales in breathing no less than 

 11 oz., of charcoal per day; whilst the vegetable king- 

 dom, far from suffering from excess of carbon, requires 

 its store to be augmented. 



Emily. Ah ! this is what I have heard spoken of as 

 one of the most beautiful dispensations of Providence : 

 the vegetable creation purifies the atmosphere, by absorb- 

 ing the carbon with which it has been contaminated by 

 the breath of animals. 



Mrs. B. Just so ; but let us examine these wonders 

 a little more narrowly, and trace the steps by which they 

 were brought to light. 



425. What further does Mrs. B. say of this analogy 1 ? 426. What 

 question does Emily ask concerning the effect produced on plants by the 

 atmospherical air so far as relates to the carbon! 427. What is the 

 reply! 428. How much carbon does a man exhale in a day! 429. 

 How is the atmosphere purified after having been contaminated by the 

 breath of animals'! 



