Page:Popular Science Monthly Volume 21.djvu/304

292 us examine this little shred with our microscope, using a lens of moderate power. This is from the upper side of the leaf (Fig. 4). How delicate the cell-walls, how beautiful the pattern! Here is Nature's best attempt at uniformity. All these cells serve identically the same purpose, and, so far as we can see, might have been exactly alike. Yet, while there is similarity, no two are just alike. Let us tear off another shred of epidermis, this time from the lower surface of the

leaf. Here (Fig. 5) we have the same arrangement and forms of cells, but more beautiful and varied outlines, and the cells are more intimately interlocked. Our magnifying power is greater, and the cells appear larger; moreover, we have before us a few cells altogether unlike any of their neighbors, little button-hole-like structures. These are the stomata of the leaf, and through these tiny mouths for the stomata are real openings through the epidermis the exchange of gases goes on between the growing plant and the surrounding atmosphere.

Let us now pass on a little further in our investigation of these plant-cells and note the contents of some of them. In our examination