Chlorophyll is plant green.
That is what the word means.
We are so used to seeing green leaves that we think very little about it.
It probably never has occurred to most of us that the green coloring matter of plants can be of much importance. Yet it is one of the most important things in the world.
Like many other things, it is not what it seems. It is not merely a dye as one might suppose, but much more than that.
We cannot really see what it is without a microscope, and when we look at a piece of green leaf through the microscope we are surprised to find the leaf is not green at all.
It is colorless like glass, but in the cells just behind the skin cells we see little roundish green bodies packed away. These are the chlorophyll grains, and when there are a great many of them close together they show through the skin and make the whole plant green.
The skin protects them, you see, and yet it is transparent and allows the light to get to them, which is a matter of great importance to the chlorophyll grains, for they are hard workers, but cannot do a single thing without sunlight.
Chlorophyll grains lie just behind the skin cells in all parts of the plant that look green. The cells they lie in are often long with their short ends towards the skin. Leaves contain several layers of chlorophyll cells. The inner ones are not long like the outer ones, and do not contain so many chlorophyll grains. In the illustration, a, a represent the upper and lower skin and b the cells containing chlorophyll. The under side of a leaf usually has fewer chlorophyll grains in its cells, for the light is not so bright there, and chlorophyll needs plenty of light.