THOSE LITTLE WORKSHOPS 89 



Like ourselves again ! But a man digests his food by 

 means of his stomach ; while a tree digests by means of 

 its leaves. 



So the leaves have to carry on two separate tasks at 

 the same time. In breathing, they capture air with its 

 life-supporting oxygen, and get rid of carbonic-acid gas. 

 But in digesting, they again capture air, and do just 

 the opposite. They keep for food the carbonic-acid 

 gas — which is more strictly known as carbon-dioxide — 

 and they get rid of the oxygen. Green plants and all 

 green portions of plants feed very largely on carbonic- 

 acid gas; for it is much needed in building up the 

 substance of a tree. 



Both men and plants in breathing make the air around 

 less healthy, because they keep taking away from it 

 oxygen gas, and adding to it carbonic-acid gas. And 

 if this went on perpetually, with nothing to undo the 

 harm, our whole atmosphere would in time become 

 impossible for us to breathe. 



But there is a something, and a very big something, 

 to undo it. There is the work of leaves, of grasses, of 

 countless millions of them in all parts of the world, taking 

 in carbonic-acid gas as food, and pouring out enormous 

 quantities of oxygen gas, so needful for life. While 

 they breathe like ourselves, thus helping to render the 

 air unfit for us to breathe, they also by their digestion 

 set the matter right, and keep the atmosphere pure and 

 good. 



They are doing it always ; but not all plants in the 

 whole world incessantly. Day after day, and month 

 after month, they carry on this work in relays. Each 



