FUNGI, fun'ji (singular Fungus, Latin name for mushroom), the general name ap plied to a multitude of lower plants of quite diverse structure, but which agree in not con taining chlorophyll, the green coloring matter of the vegetable kingdom. Formerly the fungi were regarded as constituting a natural group (class or order), but are now recognized by modern botanists as belonging to many natural groups of plants.
The peculiarities of fungi are physiological; they result from their food habits, and are not primarily structural and of profound signifi cance. When we enumerate the physiological changes involved in the change of a plant from an independent life to one of parasitism or saprophytism, we have considered all of the essential differences between the fungi and the green plants from which they have been de rived. We may say then, that a fungus is a lower plant which has suffered certain physio logical changes on account of the fact that it has become parasitic or saprophytic.
Before going farther it is necessary to de fine certain terms which must be used in any discussion of the fungi. A plant is a parasite when it lives upon or in another living, plant, absorbing food from it, and living at its ex pense. The mere fact of growing upon an other plant does not make the first parasitic, for there ate many small plants which merely find lodgment upon larger species, not, how ever, absorbing anything from the plants on which they are lodged. When it is necessary to distinguish such plants, they are called epi phytes. In the case of parasites the plant or animal upon which they live is spoken of as the host. When a plant lives upon an organism which is no longer living or upon its products it is called a saprophyte. Thus the toadstools which grow so freely on manure and other de caying vegetable matter are saprophytes. It is sometimes necessary to have a term to apply to plants which are neither parasitic nor sapro phytic, and then we use the word holophyte. Thus all common green plants are holophytes. When it is desired to contrast holophytes with both parasites and saprophytes, we can use the term hysterophyte for the parasitic and sapro phytic plants.
Applying the terms we have now defined, we may say that all fungi are hysterophytes, some living parasitically upon their hosts, others liv ing saprophytically.
All holophytes are green in color, although in many this is concealed by other pigments i and the significance of this is purely physiolog ical. Green plants absorb the gas carbon di
oxide, and in green cells this is combined with some of the elements in the ever-present mois ture of the plant into a chemical compound allied to starch and sugar, and characterized by consisting of nearly equal amounts of carbon and oxygen, combined with nearly double the amount of hydrogen.
Such compounds are known as carbohydrates and they are made by all holophytes, and then used in the processes of assimilation and growth. It has been demonstrated that plants which are not green cannot make the carbo hydrates. and since all plants need these com pounds for building up their tissues, it follows that colorless plants must obtain them by talc' ing them from living or dead, green plants. Last, it should be borne in mind that even green plants cannot make the carbohydrates in darkness. For this work they need light and in fact the greatest importance of light to a plant is in connection with this process of making carbohydrates. Accordingly plants which are not green, and which as a consequence do not make carbohydrates, often grow in darkness or in feeble light. This is quite characteristic of the fungi, great numbers of which grow as well in darkness as in light, or in some cases grow even much better in the darkness than they do in the light.
The fungi are very numerous, some recent estimates placing the number of species as high as 250,000, of which not more than one-third have as yet been described. They occur wher ever there is organic matter of any kind upon which they can subsist. Wherever there are living plants or animals there are fungi which obtain food either from the living cells of their hosts, or the dead and cast-off cells and tissues. Some species occur in the lower layers of the air, in all exposed waters and in the soil. They are the most numerous of living things when we consider individuals alone. They range in size from extremely small to many centimeters in length. The smallest are far too minute to be seen by the naked eye, some being visible only by the aid of the most powerful micro scopes. Of some of the smallest species it would require 25,000 to 30,000 placed side by side to measure one inch. On the other hand there are toadstools a foot or so in height and diameter, and puff-balls two to three feet in diameter have been recorded.