This sub-kingdom, one of the chief divisions of the vegetable kingdom, is known as the class thallophytes. It contains the simplest forms of vegetable life. Its chief groups are the fungi and algæ, the lichens being related to both, as if algæ and fungi had united in one plant, dividing and somewhat changing the characteristic of each. At any period of the year you can find lichens in abundance. They cover ragged rocks, dress up old roofs, walls, fence rails and dead stumps, especially delighting in the north side of trees. If we examine them through a magnifying glass, we shall see that they are made up of cells, laid side by side like little chains of beads, or of cells expanded into short tubes or threads lying like heaps of tiny fagots. Instead of seeds, lichens have a fine dust, called spores, from which they develop. Lichens are exceedingly long-lived and excessively slow of growth. The lily attains its lovely maturity in a few months; the oaks, elms, pines, become great trees in twenty or thirty years; the humble lichen often lives forty or fifty years before it is old enough to complete its growth by producing spores. Botanists say that the life of a lichen is fitful and strange, and is practically indefinite as to duration. Lichens simply live on and on. Some lichens have been known to live nearly fifty years without seeming to grow; they appear to dry up, and nearly vanish; then, suddenly, from some cause there is a revival of growth--they expand again. Small and insignificant as these lichens are, they often outlive those longest-lived of trees, the cedar of Lebanon and the California redwood. The condition of lichen existence is water, for from moisture alone, in dew or rain, they secure their food. The carbon, oxygen, ammonia, hydrogen, in air and rain, afford them their nourishment. The lichen generally refuses to grow in foul air laden with noxious gases. In the impure air of cities few appear, but they abound in the open country. They absorb by all the surface, except the base by which they are fastened to their place of dwelling. They have no roots, and simply adhere to bare rocks, sapless wood, even to naked glass, from which they can receive no nutriment whatever. In comparison with what is known of plants in general, our knowledge of lichens is yet very limited. They seem to be made chiefly of a kind of gelatin which exists in lichens only. Humble as they appear, they have always been of large importance in arts and manufactures. They produce exquisite dyes--a rich, costly purple, a valuable scarlet, many shades of brown, and particularly splendid hues of blue and yellow are obtained from these common little growths, which in themselves display chiefly shades of black, gray green, varied with pink, red, and orange cups, balls, and edges. FUNGI