THE DEMAND FOB FBESH AIB. 59 



The breathing pores number thousands on every carnation 

 leaf, and exist on both the upper and lower surface of the leaf, 

 which is not the case in many species of plants. They are sim- 

 ply mouths or nostrils leading down between the cells which 

 make the tissue of the leaf. Through these openings is exhaled 

 oxygen gas, and effete poisonous elements in the form of vapor; 

 and they inhale carbonic acid gas, and healthy tissue-building 

 material in atmospherical form. 



FIG. 1. Surface view of a carnation leaf under very strong magnification, show- 

 ing the epidermal cells and the round openings leading to the stomata. 



A man requires 250 cubic feet of air every hour to supply 

 his system with the needed amount of oxygen, and his blood is 

 distributed over 1400 superficial feet of cell surface in the lungs 

 to absorb from the air inhaled this essential life-giving element. 



The vegetable blood of a carnation plant is distributed over 

 an area of cell walls in its foliage a thousand times geater than 

 its leaf surface, for precisely the same purpose as in an animal but 

 with reversed function. The plant expires oxygen and inhales 

 carbonic oxide. An almost .air-tight glass house holding thous- 

 ands of breathing carnation plants would be speedily exhausted 

 of its supply of plant air and they would soon suffocate in their 

 own poisonous exhalations. 



This simple automatic arrangement of nature is open only to 

 the entrance and exit of vaporal forms. Leaves do not absorb 



