much as in the water moulds. As these structures are very minute, a droplet on a leaf is large enough for the germination of hundreds of the detached zoosporangia. Here again, the zoospores, after coming to rest, develop into new plants, which at once penetrate the host. In some species the zoosporangia grow at once into a filament, without forming zoospores.

The sexual organs of downy mildews are much like those of water moulds, the differences being quite immaterial for the present discussion. (Fig. 7.)

FIG. 7.-Peronospora alsinearum, showing antherid pen. etrating the egg-cell. Highly magnified.

FIG. 8.- Mucor stolonifer. Highly magnified.

It is evident from a comparison of the structure and reproductive organs of water moulds and downy mildews, that the latter are derived from the former. Just as the water moulds have been derived from the green plants of the green felt family (Vaucheriacea) by the adoption of parasitic and saprophytic habits, so by the change from strictly aquatic conditions to those found in the intercellular spaces of land plants, water moulds have been changed to downy mildews. Every difference between the two families may be accounted for by this difference in the environment of the plants.

Black Moulds (Mucoracea) show an additional modification of the water mould type. They are non-aquatic, mostly saprophytes, a few only being parasites. They live for the most part on dead organic matter, animal or vegetable, which is still moist, and but few species can live in the water. The commonest species live on the starchy and sugary substances in pantries, cellars, and other places where these substances are found in the presence of sufficient moisture. Organic substances which are dry are not attacked by black moulds.

Each black mould plant is a branching tubular filament, which has few cross partitions. One part of the plant usually grows in the substance of the organic matter, and another grows upward into the air. (Fig. 8.) The former absorbs food matter, while the latter bears reproductive organs, as in the water moulds. The ends of the aerial branches enlarge as in the two preceding families, but instead of forming zoospores, the protoplasm in the terminal segments forms many small spores, each covered with a cell wall. These spores are the homologues of the zoospores in previous families, but as the plants are not aquatic, these zoospores have ceased to be

aquatic also. With a good cell wall to protect their protoplasm, they may be blown about in the air without drying up. It is in this way, in fact, that black moulds are propagated, the air currents carrying the spores sometimes for long distances, and when they fall upon organic matter under favorable conditions they quickly give rise to a new crop of mould plants. the filaments which penetrate the nutrient substance, or grow over its surface, are to be found (rarely, however, in the common species) sexual organs somewhat resembling those of the two preceding families. (Fig. 9.)

On

are

Insect Fungi (Entomophthoracea) somewhat similar to black moulds, but are parasitic in the body tissues of insects, and accordingly show considerable structural modifications. (See below.) Fig. 10.

Branch Carpophyta. The Carpophytes.— The plants which constitute this immense group are of much higher structure than those in the two preceding branches. They are still typically aquatic, and so are seaweeds, but this name is not as commonly applied to them as to the Phycophytes. The typical species are green plants, but in one group (the red seaweeds) the chlorophyll is hidden by a red or purple coloring matter. The plant-body is usually composed of an axis on which are symmetrically arranged branches or leaves. The lower end of the axis is supplied with root-like organs by which it is attached to the soil or other support, and the plant commonly stands upright. Some species show a wonderful beauty of form and color, and on this account are greatly prized by amateur botanists, who collect and preserve them under the name of sea mosses.

All Carpophytes reproduce by two common methods. In the first, certain end cells separate from special branches, and float away to germinate and grow directly into plants like those from which they came. In the second method of reproduction an egg-organ, much like that of

FIG. 9.- Mucor fusiger; A, young sexual organs; B, after fertilization. Highly magnified.

the Phycophytes, is fertilized by spermatozoids from an antherid which, again, does not differ in any essential respect from that of the Phycophytes. However, the result of the fertilization is the formation of a more or less compound body which the botanist recognizes as a primitive kind of "fruit." Hence, the aquatic Carpophytes are sometimes known as "Fruit Tangles." In these fruits are spores, and these on escaping and germinating give rise to new plants.