Page:Popular Science Monthly Volume 21.djvu/303

This page has been proofread, but needs to be validated.

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

PSM V21 D303 Unicellular alga.jpg
Fig. 2.—Unicellular Alga (copied from Thomé.)

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