=431. A very general outline of classification=,[19] according to the former of these views, might be presented here to show the general relationships of the fungi studied, with the addition of a few more in orders not represented above. It should be borne in mind that the author in presenting this view of classification does not necessarily commit himself to it. It is based on that presented in Engler & Prantl’s Pflanzenfamilien. There are three classes. [19] =Class Myxomycetes=, or =Mycetozoa=.—To this class belong the “slime molds,” low organisms consisting of masses of naked protoplasm which flows among decaying leaves and in decaying wood, coming to the surface to fruit. The fruit in many cases resembles miniature puff-balls, and these plants were formerly classed with the puff-balls. The spores germinate by forming swarm spores which unite to form a small plasmodium, which in turn grows to form a large plasmodium or protoplasmic mass. It is doubtful if they are any more plant than animal organisms. Examples: Trichia, Arcyria, Stemonitis, Physarum, Ceratiomyxa, etc., on rotten wood; Plasmodiophora brassicæ is a parasite causing club foot of cabbage, radishes, etc. It lives within the roots, causing large knots and swellings on the same. [Illustration: Fig. 249. Chytrids. _A_, Harpochytrium hedenii, parasitic on spirogyra threads; _a_, sickle-form plant; _b_, the sporangium part with escaping zoospores; _c_, old plant proliferating by forming new sporangium in the old empty one; _d_, zoospore; _e_, two young plants just beginning to grow. _B_, Rhizophidium globosum parasitic on spirogyra. Globose sporangium with delicate threads inside of the host, zoospores escaping from one. _C_, Olpidium pendulum, parasitic in spirogyra cell. Elliptical sporangium with slender exit tube through which zoospores are escaping. _D_, Lagenidium rabenhorstii parasitic in spirogyra cell. Two slender sporangia with exit tubes through which protoplasm escapes forming a rounded mass at the end of tube, this protoplasm forming biciliate zoospores.] I. Class Phycomycetes (Alga-like Fungi). 1. SUBCLASS OOMYCETES. =432.= These are the egg-spore fungi. They include the water mold (Saprolegnia), the downy mildew of the grape (Plasmopara), the potato blight (Phytophthora), the white rust of cruciferous plants (Cystopus = Albugo), the damping-off fungus (Pythium), and many parasites of the algæ known as chytrids, as Olpidium, Rhizophidium, Lagenidium, Chytridium, etc. The two following orders are sometimes placed in a separate subclass, _Archimycetes_. [Illustration: Fig. 250. Monoblepharis insignis Thaxter. End of hypha bearing oogonium (_oog_) and antheridium (_ant_). Sperms escaping from antheridium and creeping up on the oogonium. (After Thaxter.)]