Page:Popular Science Monthly Volume 21.djvu/303

Rh stem, roots, and branches of higher plants, some are tiniest rolling spheres; some stretch away to the length of several feet, and some are microscopic specks. In Fig. 2 we have the representation of a beautiful marine alga, unicellular, and yet thirty inches or more in length.

As we ascend the scale of life we find the individual cell more subordinate to the organism as a whole, and so less complex in itself; and



yet, when we examine the cells which make up the tissues of the best plants we can find, the blooming occupants of our hot-houses, gardens, and fields, we meet with marvelous diversity, and are soon made to feel that variety of form is the law, uniformity the exception. Fig. 3 represents the appearance of a cross-section of a stem of Tradescantia. From this section we may learn not the variety of cell-forms only, but something of the manner in which every plant is developed, and something of the porousness of all cellular structure.

But let us tear off with our forceps a little shred of the epidermis of some leaf. The leaf from a petunia will do; that of the wild Jacob's ladder is better, and that of the wake-robin better still. Let