mense aggregation of many thousand species (16,000 or more), of which we know but one stage (apparently the first) and so are unable to assign them to their proper place in the system. They are minute and mostly parasitic plants, occurring in the tissues of higher plants, and sending their spore-bearing branches out into the air. Some plants formerly placed here have been found to be early stages of certain sac fungi (black fungi, or their relatives) and it is suspected that most, if not all, of them will eventually be so disposed. At present they are grouped under three general kinds, as follows:

Spot Fungi (Sphæropsidaceae), which produce whitish or discolored spots, and later develop closed, spheroidal cases, containing free spores. Septoria and Phyllosticta are common genera. Toqque le

FIG. 24. Basidia in different stages of development; A, when very young; B, with the spore-branches beginning to form at the summit; C, showing the spore-branches with nearly mature spores at their ends. All highly magnified.

Black-dot Fungi (Melanconiacea) are like the spot fungi, but there are no spore cases, the spores developing in masses beneath the epidermis which they eventually rupture. Glæosporium is a common genus.

Molds (Moniliacea and related families) produce their spores on branches which grow out through the stomata of the host. Here we find the parasitic species of Ramularia Cercospora, etc., and the mostly saprophytic species of Monilia. Botrytis, etc.

Basidium Fungi (class Basidiomycetea). -The distinguishing mark of this class is that the spores are produced externally upon clubshaped or rounded terminal cells. (Fig. 24). These club-shaped, spore-bearing cells are technically known as basidia (singular, basidium), whence the scientific name of the class. The basidia of this class are regarded in this discussion as the homologues of the spore-sacs (asci) of the preceding class.

About 14,000 species of fungi of this class are known. Many attain to considerable dimensions, especially their fruits. They are typically saprophytic, but it is now known that many of them are more or less parasitic, also, when the opportunity offers.

FIG. 25. Two species of puff-balls; A, Lycoperdon cælatum; B, Lycoperdon gemmatum.

wood or earth rich in organic matter, and finally produce globular fruits which rise above the surface. (Fig. 25), These fruits are filled with tortuous canals whose walls are studded with basidia on which the spores are produced. At maturity the interior tissues of the fruits deliquesce, setting free the spores, which escape into the air a little later as a dusty cloud, by the rupture of the fruit wall. From these spores new plants are produced, but we do not know the whole life history of these common fungi. Although the sexual organs should precede the formation of the fruits, they have not yet been observed.

Stink-horns (Phallacea) are closely related to the puff-balls, which they closely resemble in all stages excepting the last. Here the sporebearing portion of the globular fruit is confined to a vertical, circular layer of tissue about midway between the centre and the circumference. At maturity the spore-bearing tissues deliquesce and at the same time the tissues below rapidly elongate, bursting the fruit-wall and carrying up the spores into the air. (Fig. 26). These fruits have very bad odors, which attract insects, and it is thought that these help to distribute the Tootebro Isad

FIG. 26.-A, a stink-horn (Phallus impudicus) after the rupture of the volva; B, highly magnified section of the spore-bearing layer.

spores. Stink-horns are from an inch or two to six or more inches in height, and grow commonly in lawns and pastures, where their presence is indicated by their intolerable odor.

FIG. 27.- Development of a toadstool (Amanita muscaria) shown in vertical section. A, very young stage; B and C, later stages; D, after the bursting of the volva. Most species are saprophytes, but some are parasites. When the fruits are young they resemble those of puff-balls, but as they grow older a circular layer of spore-bearing tissue develops, and this, by the rapid growth of lower lying tissues, is carried up on a stalk, very much as is done in the stink-horns. (Fig. 27). Here, however, the stalk is formed earlier, and the spores are usually developed after the rupture of the fruit-wall.

A typical toadstool fruit has the following structure: There is first at the bottom the cupshaped remnant of the original fruit-wall (technically, the volva); from this rises the cylindrical stem (stipe), terminating in an expanded cap (pileus). The stem and cap together resemble an expanded umbrella, or a one-legged stool (Figs. 28 and 29), from which latter fact the common name "toadstool" was doubtless suggested. The lower surface of the cap is folded into many vertical radiating plates, called gills (lamella), and these are studded with the basidia, bearing the spores. This gill portion corresponds to the circular spore-bearing layer of the stink-horns, and the gills themselves are to be regarded as devices for increasing the number of spores, by an enenlargement of the surface studded with basidia.

While in typical toadstools the cap is rounded and centrally attached to the stem, in

FIG. 29. Agaricus campestris, the cultivated mushroom, showing several stages of development.

so common on decaying logs and other forms of timber.

Some pore fungi are fleshy, but for the most part they are hard and tough, often resisting decay for many years. Some of the species are perennial, adding successive layers of pore tissue to their fruits for some years.

ECONOMIC RELATIONS OF FUNGI.

The economic relations of the fungi are of great importance. Some are edible and furnish wholesome food to man and other animals, some are used in the arts, some yield medicines, some are the cause of disease in man and other animals, and some again attack and destroy other plants, including many of the cultivated plants of our farms and gardens.

Edible Fungi.- Here perhaps we should include those bacteria which have to do with the flavor of butter and cheese, and those molds whose presence in cheese adds to its edibility. Of far greater importance, however, are those species which are eaten for the nutriment which they contain. Truffles are collected in Europe, and sold in the markets. Dogs and pigs are trained to search for them, the attendant bagging the truffle when found by the keen scent of the animal. The Morels are sac fungi