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 kind, 
whose seed is in itself, upon the earth, — and it was so ? The answer to these ques- 
tions will show us plainly 
279. What Plants are made for. In the first place, in the very act of making 
vegetable matter, 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 oxygen 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 carbonic acid is the very 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 which 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. They 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 herbage, or more concentrated in the accumulations of 
nourishment which 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 fond 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 w r ays what plants have prepared for them. But however received, and how- 
