Page:Popular Science Monthly Volume 6.djvu/355

Rh something like these in all the substances we are going to examine. They are called cells. Sometimes cells are quite colorless and clear or transparent, but here you see they are colored—some are green, some red, and others are red in the middle and green at the border. You will notice that this coloring is all inside the cell, and not in the wall or outside, cover of the cell; and sometimes, though not often, you can see this coloring-matter is formed in little grains. Now I wish you to

notice the size and shape of the cells. You will find that most of them are from 1/3000 to 1/2500 of an inch in size, and nearly all of them have a round shape. Let us see now how many different things we can find in these cells. First, there is the outside cover or sac; this sac seems to be filled with something that looks like jelly, or the white of an egg, and in this jelly you can see the green and the red colored grains, a little round, hard-looking body that looks like a kernel, and sometimes in the middle of the sac there is a thin, empty-looking space. We will begin at the outside and look at each of these things separately, and try to find out what they are. If you press some of the

cells lightly they will burst, the soft inside part will flow out and leave the empty sac just the shape of the cell except where it is torn. This shows that the outside is much stronger and tougher than the inside. Chemists have found that this wall of the cell is made exactly the same as the tough cells of wood—it is called cellulose.

The light-colored jelly inside the sac has a long name of its own—protoplasm—which means first form or mould, because this seems to be the first form of all life. The green and the red colored grains are called chlorophyll. The word means green leaf. But chlorophyll is not always green: as you see in this mould, it is sometimes red, and it has many other colors; nor is it found in leaves only, as you will see when we come to study the stems and flowers of plants. But this dye-stuff or coloring-matter was first found in the leaves, hence its