They differ from lichens mainly in deriving their sustenance from the object on which they grow (though this has exceptions), in not producing a foliaceous thal-lus, and in not forming green chlorophyl; from algae, in being aerial, not aquatic, and in deriving their nourishment from their matrix and not from the surrounding medium. Those species of fungi which are found in fluids, such as the yeast and vinegar plants, are now proved to be merely submerged mycelia of certain moulds (penicillium), which do not attain their perfect stage until they reach the air. Their propagation in fluids is due to a power the mycelium possesses of retaining its vitality under a variety of circumstances, of suffering division and enduring extremes of temperature. Besides this, it has a propagating power analogous to that of budding. In some aerial forms it goes on reproducing itself in peculiar ways, and rarely reaching the normal or perfect as-cigerous fructification. For this reason many species have been thought to be distinct plants when they are merely arrested stages of growth of one single species. Some aerial forms never reach a further growth than a compact, dense mass of mycelium.

Oak trees sometimes contain a solid mass of a leathery texture (xylostroma giganteum), which never advances beyond that stage. The genera sclerotium and rhizomorpha, with their so-called species, are mere compact bodies of mycelium, which have in some instances been artificially forced to develop themselves, and have produced plants of widely different structure. The ergots of grain are the ovary arrested in its proper development and transformed into a peculiar growth by the presence in its tissues of a minute fungus. Tulasne and others have watched their development into species of cordyceps. These forms remain constantly arrested; but very many of those which under favorable circumstances reach perfection remain similarly checked, and confuse the student with their multiple forms. This has caused the naming of hosts of species which are merely forms of others. There is no branch of science whose synonymy is more burdensome. It is almost a hopeless task to attempt to identify the species of authors by description alone, the plant itself being necessary for comparison. Long and continued observations are required to determine and connect the many forms which a single fungus may assume in the course of its existence.-Few objects in nature exhibit more gorgeous colors.

The larger fleshy forms present an endless variety of graduated tints. Some of the boleti exhibit on being broken a remarkable change of color, the white or yellowish hue of the interior changing instantly to a vivid blue. This is supposed by Prof. Robinson to be due to a molecular and not to a chemical change. Their texture is as variable as their color. Some are almost fluid, others fleshy, papery, leathery, corky, or hard and horny. Their size is equally various, from mere specks to masses some feet in girth. Their rapid growth is astonishing. Puff-balls sometimes grow 6 in. in diameter in a night. Masses of paper pulp thrown out hot from a vat have been found within 24 hours filled and swollen with a species of agaricus. Schweinitz records the growth of a species of oethalium found on a piece of iron which was heated the night before in a forge. Some of the ephemeral coprini grow up in a night and melt away in the morning sun. Other species, like the poly-pori, grow very slowly and add a new layer every year, covering that of the previous season. Their expansive force in growing is very great.

Notwithstanding their soft, yielding texture, agarics are able to raise heavy stones under which they spring up; Bulliard tells of a phallus which burst a glass vessel in which it had been confined; and a case came under the writer's observation in which a puff-ball broke up through an asphalt walk that had been long established and well hardened. Their sudden occurrence over wide districts depends upon peculiar states of the atmosphere favorable to the development of the spores. They generally appear in the greatest abundance in moist autumn weather, though some are found wherever there is moisture. Some depend so much on peculiar states of the atmosphere that they appear suddenly and then disappear for a' while. The pustular forms, however, which abound on the dead bark of trees, shrubs, old stumps, and fallen twigs, are more durable from their more solid structure. Some species of agaricus possess a remarkable luminosity, and certain rhizomorploe growing in mines shed a phosphorescent light of extreme brilliancy. Fungi differ from flowering plants in their chemical influence upon the air. They absorb oxygen and exhale carbonic acid, performing the same office in this respect as animals, which they most resemble in chemical composition, in being highly azotized.

The odors they emit in decay are more like putrescent animal than vegetable matter. The fleshy sorts generally possess a peculiar earthy odor, but some species of phallus and clathrus emit a most intolerably offensive stench, which will render a close apartment untenantable. Others, on the contrary, are very agreeable to the smell, and some in drying acquire a fine aroma. They are quite as variable to the taste. The prevailing flavor is rather negative and peculiar to the order; but they are also bitter, acrid, biting, astringent, oily, and nauseous, as well as savory and agreeable. Most of them lose these qualities in drying.-Fungi have been used as an article of food from remote antiquity. The writings of the ancient's make frequent mention of them as among their most esteemed viands. They are extensively eaten in Europe by all classes, and many works have been written laudatory of their virtues, with copious directions for dressing them in a great variety of ways. Notwithstanding the virulent poisonous qualities of some, others are eagerly sought for, and in some places it is said that the people have burned down woods to get certain species of fungi whose growth followed the combustion.