90 WHY PLANTS GROW, 



plants have been making, day by day, since God said, Let the earth bring forth 

 grass, and the herb yielding seed, and the fruit-tree yielding fruit after his hind, 

 whose seed is in itself, upon the earth, ■ — and it was so ? The answer to these ques- 

 tions will show us plainly i 



279. What Plants are made for. In the first place, in the very act of making 

 vegetable mattei-, plants fulfil one great purpose of their existence, that is, 



280. They purify the air for animals. That part of the air which renders it fit 

 for breathing is called oxygen ; this makes up about one fifth part of the air we 

 breathe. At every breath animals take in some of this oxygen and change it 

 into carbonic acid ; that is, they combine the oxygen with carbon from their blood, 

 which makes carbonic acid, and breathe out this carbonic acid into the air, in place 

 of the oxygen they drew in. Now this carbonic acid is unfit for the breathing of 

 animals, — so much so, that, if it were to increase so as to make any considerable part 

 of the atmosphere, man and other animals could not live in it. But plants prevent 

 the carbonic acid from accumulating in the air. While animals need the oxj-gen of 

 the air, and in using it change it into carbonic acid, hurtful to them, plants need the 

 carbon of this carbonic acid ; indeed, it makes a very large portion of their food, — 

 as we plainly see it must, when we know that about half of every part of a plant is 

 carbon, that is, charcoal. And this ca]-bonic acid is the vei-y part of the air that 

 plants use ; they constantly take it from the air, decompose it in their leaves during 

 sunshine, keep the carbon, and give back the oxygen pure, so keeping the air fit 

 for the breathing of animals. The carbon wdiich plants take from the air in this 

 way, along -with water, &c., they assimilate, that is, change into vegetable matter : 

 and in doing this 



281. Tliey make all the food which animals live upon. Animals cannot live upon 

 air, water, or earth, nor are they able to change these into food which they may 

 live upon. This work is done for them by plants. Vegetable matter in almost 

 every form — especially as hei-bage, or more concentrated in the accumulations of 

 nourishment wdiich plants store up in roots, in bulbs and tubers, in many stalks, 

 in fruits, and in seeds — is food for animals. "And to every beast of the earth, and 

 to every fowl of the air, and to everything that creepeth upon the earth," as well as 

 to men, is given " every green herb for meat." Some animals take it by feeding 

 directly upon vegetables ; others, in feeding upon the flesh of herbivorous animals, 

 receive what they have taken from plants. Man and a few other animals take in 

 both ways what plants have prepared for them. But however received, and how- 



