28 SAGACITY AND MORALITY OF PLANTS. 



formed into the wood of the tree or shrub, the starch 

 of the potato or bulb, or the sugary matter of the 

 beet, carrot, parsnip, and sugar-cane, and honey of 

 the nectaries of flowers. 



Let us now return to consider the nature and 

 function of the chlorophyll^ the chief substance 

 secreted in the leaves of plants. An enlarged 

 section of a leaf shows us the cells packed away, 

 each containing the minute green grains of this 

 important material. It is to the presence of chloro- 

 phyll in the cells that the greenness of all vegeta- 

 tion is due. 



Everybody knows that the air we breathe is 

 tainted with carbonic acid, cast into the atmosphere 

 from the breath of the untold millions of men and 

 animals inhabiting the globe. It has been calculated 

 that at least forty-five millions of tons of carbonic 

 acid are thus thrown into the atmosphere every day ! 

 This has been going on during all geological time ; 

 it will continue until the " last man " and the last 

 animal has passed away into extinction ! 



Evidently, if there were no means of getting rid 

 of this poisonous gas, the atmosphere would very 

 speedily be unfit for animals to breathe. Here it is 

 that the services of plants are conspicuous, apart 

 from the food they supply to the animal world. In 

 the daytime, and especially when the sun is shining, 

 the myriads of stoinata on the under -surfaces of 

 leaves are all at work. The stomata are then wide 



