34 ON SOME RESEMBLANCES BETWEEN PLANTS AND ANIMALS. 
and it has an apparatus specially formed to enable it to obtain 
air; and if through the clogging up of its breathing apparatus it 
cannot obtain a due supply, it becomes literally suffocated like an 
animal. 
The part of a plant which corresponds to an animal’s lungs are 
its leaves. If you examine a leaf, you will first of all see that it 
is spread out very flat and thin ;—that is in order that a very large 
amount of surface may be exposed to the air. You will find that 
the surface of the leaf is covered with a delicate skin, easily 
separated in some plants, not so easily in others. If you look at 
this skin through a microscope you will see that it is studded 
with immense numbers of small green openings. A more careful 
examination would show that these ‘‘stomata,”’ as they are called, 
are capable of opening and closing to admit the entrance and exit 
of air and various gases. It is through these openings that air is 
admitted into the substance of the leaves, where it acts upon the 
sap that I have already told you found its way to the leaves, and 
works those changes upon it that can only be compared to the 
changes that take place in the blood of animals when it comes in 
contact with air in the lungs. 
The whole subject of the respiration of plants, and its relation 
to that of animals, is too’ long to enter upon now, and it is also 
unnecessary for the purpose of this paper; but it is a subject of 
peculiar interest, and brings before us some of the most wonderful 
facts in botany with which we are acquainted. 
Powers of motion and locomotion are by no means confined to 
the animal kingdom. Indeed there are many animals that are 
as firmly fixed to the places where they grow as plants are, and 
cannot change their position at all, and whose only possible 
powers of motion are opening and shutting their mouths to receive 
the food that is washed past them, and almost forced upon them. 
Many plants are capable of as much motive power as this, and 
some of far more, and I will now give a few instances of move- 
ments in plants that are interesting. 
There are several plants that move when touched, as the 
Sensitive Plant, and parts of the flower of some Orchises, and these 
