Page:Popular Science Monthly Volume 6.djvu/357

Rh oxygen to the air again. Thus he works from sunrise to sunset. His hours are regulated by the sun, instead of by Congress. You never hear of an "eight-hour movement" or a "strike" among the chlorophyll laborers. As soon as the sun goes down they go to bed, like honest workmen. During the night, while these green-leaf or chlorophyll workers are asleep, the colorless protein-jelly of the cell gives out the poisonous carbonic acid and takes in oxygen. The green cells give off carbonic acid and take in oxygen during the day, as well as during the night, but the little chlorophyll-grains do so much more work than the rest of the jelly in the cell, it seems as though the cell gives out nothing but oxygen and takes in nothing but carbon during the day, when all these little colored chemists are doing their best.

Now you can understand why it is healthy to have growing plants in your room during the day, but not during the night. When the sun is shining they purify the air, because they give off more oxygen than carbonic acid; but at night they poison the air, because they give off only carbonic acid.

All plants that contain this green-leaf matter, or chlorophyll, are called green plants. You remember the colorless plants, such as toad-stools, are called fungi. It is found, as you have seen, that green plants must have the sunshine, but fungi grow as well, or even better, in the dark. Thus we have found the materials out of which the mould-cell is made, and the use of all its different parts. Who would have thought there was so much to learn in one of those little bladders, when you first looked at it under the microscope! This green mould-plant has a very pretty name of its own—protococcus. The word means first berry. Perhaps this name was given because these cells look like little berries.

If you look long and carefully, you can see the protococcus or berry-cell begin, like a little carpenter, to make a partition-wall right through the middle of the old house (Fig. 7); and, when the wall is finished, the two halves move away from each other, the carpenters