412 THE UNIVERSE. 



CHAPTEE III. 



THE RESPIRATION OF PLANTS. 



The largest animals — the whale, the rhinoceros, the 

 ostrich, and also man — only respire air by one channel, 

 and it is in a certain degree in one retort, the lung, that 

 all the chemical reactions of their respiration are effected. 

 In this respect plants are better provided for than is gen- 

 erally sup230sed. Instead of one sole apparatus, the mi- 

 croscopic laboratories in which their pneumatic combina- 

 tions are mysteriously carried out, may be counted by 

 thousands of millions; a single leaf sometimes presents 

 more than a million in its interstices. 



Leaves are in fact only the lungs of plants. The mi- 

 croscope discovers on their surface a crowd of elongated 

 openings, with swollen edges and not unlike the button- 

 holes of our dress. These are the stomates, or open 

 orifices by which the air enters the respiratory chambers. 

 Of extremely restricted size, owing to their being in the 

 thickness of the leaf, these invisible little chambers are 

 hollowed out in the cellular tissue, and their roofs are 

 supported by fine colonnades of cells placed end to end, 

 the marvellous labyrinth of which is traversed by the air. 



Some aquatic plants, which live in the depths of the 

 rivers, do not present this organization. Having no con- 

 nection Avith the atmosphere, these aerial cavities would 

 be of no service; hence they display quite a peculiar arrange- 



