In some of these bracket fungi, each ring on the upper surface marks a year’s growth as in the pine polyporus (P. pinicola). In the birch polyporus (P. fomentarius) the tubes are quite large. It also occurs on other trees. The beech polyporus (P. igniarius, also on other trees) often becomes very old. I have seen one specimen over eighty years old. Not all the tube-bearing fungi are bracket form. Some have a stem and cap (see fig. 245). Some are spread on the surface of logs. [Illustration: Fig. 246. Coral fungus. Hydnum coralloides, spines hanging down from branches.] =427. Hedgehog fungi (Hydnaceæ).=—These plants are bracket in form or have a stem and cap, or are spread on the surface of wood; but the finest specimens resemble coral masses of fungus tissue (example, Hydnum, fig. 246). In most of them there are slender processes resembling teeth, spines or awls, which depend from the under surface (fig. 247). The fruiting surface covers these spines. =428. Coral fungi or fairy clubs (Clavariaceæ).=—These plants stand upright from the wood, leaves, or soil, on which they grow (example, Clavaria). The “coral” ones are branched, while the “fairy clubs” are simple. The fruiting surface covers the entire exposed surface of the plants (fig. 248). [Illustration: Fig. 247. Hydnum repandum, spines hanging down from under side of cap.] [Illustration: Fig. 248. Clavaria botrytes.] CHAPTER XXII. CLASSIFICATION OF THE FUNGI. =429. Classification of the fungi.=—Those who believe that the fungi represent a natural group of plants arrange them in three large series related to each other somewhat as follows: The Gonidium Type or Series. The number of gonidia in the sporangium is indefinite and variable. It may be very large or very small, or even only one in a sporangium. To this series belong the lower fungi; examples: mucor, saprolegnia, peronospora, etc. The Basidium Type or Series. The number of gonidia on a basidium is limited and definite, and the basidium is a characteristic structure; examples: uredineæ (rusts), mushrooms, etc. The Ascus Type or Series. The number of spores in an ascus is limited and definite, and the ascus is a characteristic structure; examples: leaf curl of peach (exoascus), powdery mildews, black knot of plum, black rot of grapes, etc. =430.= Others believe that the fungi do not represent a natural group, but that they have developed off from different groups of the algæ by becoming parasitic. As parasites they no longer needed chlorophyll, and consequently lost it. According to this view the lower fungi have developed off from the lower algæ (saprolegnias, mucors, peronosporas, etc., being developed off from siphonaceous algæ like vaucheria), and the higher fungi being developed off from the higher algæ (the ascomycetes perhaps from the Rhodophyceæ).