Ferns, while cryptogamic I'n their flowerless condition, agree with the Phanerogamia in having stems and leaves; they are therefore intermediate in their structure; the transition forms leading from the simple water-plants, mushrooms, etc., to the pines and oaks.
ALGAE.
No class of plants is more interesting than the Algae. Notwithstanding their very simple structure, they offer every variety of shape, size, and color. While many of them are very minute, the beauty of their form, the delicacy of their structure, and their exquisite coloring, never have failed to attract the attention of the microscopist. The Confervoidae, or green Algae, are widely distributed, every pond, ditch, spring, and stream having representatives. The greenish matter seen on old trees, that found in bogs, the slime on stories in ponds, the silk-like threads of troughs, the sea-weed usually seen in marine aquaria, as well as innumerable other examples which might be given, serve to illustrate the green Algae, or Confervoidae. Among the green Algae we find the simplest and smallest of plants, the Chlorococcus viridis (Fig. 87), which, when aggregated in hundreds of millions, composes the greenish matter clothing in layers old trees, wood palings, etc. The Chlorococcus is a simple cell filled with granular contents. Under favorable circumstances each cell divides into halves (Fig. 88), each half becoming a new individual; this process may be continued indefinitely: such is the simple manner of reproduction in this very minute plant. Among the unicellular green Alga; are included the Desmidiaceae, which are found most often in open situations, as in the pools of bogs and moors. They are among the most beautiful of microscopic objects. Their most characteristic feature is that of bilateral symmetry, giving the impression
