O 



86 THE UNIVERSE. 



Sch nl tz even says that in certain cases these vessels may be 

 seen contracting so as to force onward the particular juices 

 which they contain. 



CHAPTER 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 lungs, that 

 all the chemical reactions of their respiration are effected. 

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

 erally supposed. Instead of one sole apparatus, the micro- 

 scopic laboratories in which their pneumatic combinations 

 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 micro- 

 scope discovers on their surface a crowd of elongated open- 

 ings, with swollen edges, and not. unlike the button-holes 

 of our dress. These are the stomata, or open orifices by 

 which the air enters the respiratory chambers. Of ex- 

 tremely restricted size, owing to their being in the thick- 

 ness 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 



