POPULAR BOTANY. 461 
important process the equilibrium of the constituents of the air will be 
restored and preserved for ever ! 
The facts stated in the foregoing demonstration will clearly show 
that, and for what reason, the atmospheric air in the country and in the 
woods must be purer and more wholesome than that of densely popu- 
lated cities ; and that the trees are very instrumental in this action. 
Furthermore, they prove that the shade trees in our cities should not 
only be regarded as sheltering ornaments, but also as benefactors to our 
sanitary welfare. The consequences will, therefore, be entirely different, 
when we keep our shade-trees sound and enable them thereby to 
perform their duty as air-purifiers — or allow rotten trees, or even stumps, 
in our streets, which, besides their disgusting appearance, consume 
oxygen gas, ard will produce dangerous miasmas in return. And these 
are the reasons why I have tried so frequently in the last five years to 
lead the attention of the public to the poor condition and the constantly 
increasing mortality of our shade-trees, and why I have ever been in a 
state of war against the destructive measure-worm ! 
Another very interesting phenomenon in connection with vegetable 
life is that which we term growth. This is certainly one of the greatest 
wonders in creation ; and if this fact does not more seriously attract 
our attention, the reason is to be found in its familiarity. Let us suppose, 
however, that a certain person had never seen a tree, and some one 
should step forward with an acorn in his hand and endeavour to make 
him believe that this small, lifeless object, when planted in the ground 
would become alive and commence to grow. After a while it would 
send out a root that grows into "the ground, and a stem that grows into 
the air. The latter would gradually extend in size until it reached 100 
feet and more. It would alfo bring forth branches, twigs, leaves, 
flowers and fruits, exactly of the same shape as that in his hand ; and 
from the latter another would spring up, and it would go on in such 
succession for all time to come ! Would such a person believe the 
assertions, although all that was said about this acorn was the truth — 
nothing more than the very truth ! 
You are all sufficiently acquainted with the phenomenon which is 
called growth ; the explanation of this process, however, is somewhat 
difficult to comprehend. I will, therefore, confine myself to the descrip- 
tion of the practical effects connected with the growth, and will com- 
mence with the very seed-grain. 
The seed in general is composed of che germ, the cotyledons, and an 
external coat. The germ is the embryo of the future plant; the 
cotyledons serve as protection and as a supporter, and the coat as a 
covering to keep the cotyledons together. In the embryo the disposi- 
tion of the future root and stem is already existing, and the cotyledons 
contain some albumen or amylum. The seed-grain, after having re- 
mained some ti me in close contact with the damp soil, absorbs so much 
