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 wherever 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 microscopes. 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.

The fungi as thus described are found in four of the grand divisions (phyla) of the vegetable kingdom.

Phylum, Myxophyceæ. The Slime Algæ. Here are gathered a thousand or so species of microscopic aquatic plants in which the cells have a very low organization. No distinct nucleus is present, and the coloring matter in the typical plants pervades the whole cell, and is of a bluish or brownish-green color instead of a bright green as in higher plants. They reproduce by simple fission, and by the production of spores. There is no hint of any sexual reproductive process. They occur in ponds, pools and streams, to which they give a greenish color by their great numbers. In decaying they usually give off a fetid odor.

While the typical Slime Algæ are greenish — and are known as green slimes-many have become parasitic or saprophytic, and have lost their green color. These colorless species are known as Bacteria, and are the lowest of the fungi.

Bacteria (Fig. 1) are then to be regarded as colorless green slimes, their lack of color

coccus, Staphylococcus, Sarcina, etc. Other bacteria consist of cylindrical cells which tend to adhere end to end in filaments or rods. In the genera Bacillus and Bacterium the rods are straight or little curved, and short or of moderate length, while in Vibrio and Spirillum the rods are more or less spirally curved. In still other genera, as Crenothrix, Leptothrix, etc., the rods are elongated. The study of Bacteria

FIG. 2.-A, Olpidium brassica, one of the simplest of the fungi (Synchytriaceae), parasitic in cells of a crucifer: B, three zoospores. Highly magnified.

in relation to diseases of man and other animals and of plants, and to soils, etc., has developed into the science of Bacteriology (q.v.). Many botanists now, on that account, do not include Bacteria among the Fungi. See BAC

TERIA.

Phylum Chlorophyceæ and Phylum Siphonophyceæ. These plants, of which there are probably nearly 2,500 species, may very properly be called sea-weeds, since they are typically aquatic, living in the salt and fresh waters of the earth. Typically they are bright green, and the cells of which they are composed have well-formed nuclei. However, the chlorophyll is confined to definite portions of the protoplasm, and is not diffused throughout the cell. Some of the lower species are spherical, rounded cells, but for the most part they consist of filaments of cylindrical cells, or in some instances they are masses of cells constituting leafy-stemmed plants. They reproduce by fission as in the Slime Algæ, but in addition all, or nearly all, Slime Algæ reproduce sexually also. In the simplest cases of sexuality, two equal and similar cells detached from older plants fuse into a new and larger cell, and then this new cell grows into a new plant. Sometimes the new cell becomes covered with a thick wall, and for a time ceases activity as a "resting spore," before it develops into a new plant.

While most of the plants of these two phyla are green plants, several hundred species have become parasitic or saprophytic in habit (Figs. 2 to 10) and have therefore lost their color, and become fungi. Among these are the following families, namely:

Gall Fungi (Synchytriacea) are beyond reasonable doubt to be regarded as hysterophytic forms of the one-celled class (class Protococcoidea) of the first of these two phyla. These fungi consist of single cells which enter the cells of their living host plants and there enlarge, feeding on the host cells and causing an irritation of the tissues which often causes swellings which may be minute or in some cases very large (e.g., wart disease of potato tubers caused by Synchytrium endobioticum). The fungus cell eventually breaks up internally into numerous minute zoospores which escape