Page:Popular Science Monthly Volume 41.djvu/216

204 hours of patient labor which it cost to bring out so much, as one little turn of the inner canal whose windings hold the living and active part of the plant, and also the explanation of the manner in which it moves. He has studied the mechanism of several forms and made models of plaster of Paris, and others of wire. Pinnularia major (see Fig. 2) is the plant from which the most conclusive results were obtained, and he claims to have demonstrated the existence of apertures on the surface of the shell through which the protoplasm may protrude. He does not, however, claim to have actually seen the protoplasm on the outside of the shell, but holds that, according to other known facts, it must be forced out, though in very small quantities. These apertures do not open directly into the interior, but by a series of winding canals whose action prevents the too easy expulsion of the contents. The movement of this protoplasm along the lines between the openings causes the movement of the diatom in a similar manner to the action of the fins of fishes. All this labor, after all, has reference only to a certain class of these plants; there are many others of such different forms that much study will yet have to be expended on them before their secrets are laid bare.

There are some curious little forms which grow in clusters on stem-like bodies which are often fastened by their other extremities to some object in the water. Some of these are shown in Figs. 6 and 7; and, finally, a variety of miscellaneous forms may be seen in Fig. 8.

There are large collections of these plants in nearly all the large herbaria of Europe, and the manner of preparing them for such collections may almost be said to form a special branch of industry. Experts are able to mount and arrange in order hundreds of these little organisms under a circular cover-glass of about five eighths of an inch in diameter. The dexterity which these experts acquire in the use of instruments is something almost as marvelous as the organisms themselves. It must be remembered, however, that this mechanical labor has nothing to do with the work of the scientist who studies the plant. It would be impossible for an investigator to give enough time to enable him to acquire this skill. A gentleman in Wedel, Holstein, has acquired a great reputation in this kind of work, and has plates holding from four to sixteen hundred different forms. These cost from twenty dollars upward, and he has recently finished a plate