. La morphologie comparative et de la biologie des champignons, bactéries et mycetozoa . La morphologie des plantes ; Champignons ; myxomycètes ; bactériologie. Chapitre VII-PHÉNOMÈNES DE VÉGÉTATION.-parasites. 361 spores. ; ils apparaissent dans la nature plutôt que les excroissances épiphytes sur les murs de cavités dans le corps des animaux qui sont facilement accessibles de l'extérieur, tels que les passages de l'oreille et les bronches. Dans la plupart des cas, la spore du parasite commence l'émission d'un tube germinatif indépendamment de l'hôte, soit après l'absorption de l'eau simple ou par crédit en même temps de la nourriture-matériel produit à l'extérieur de l'ho

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. Comparative morphology and biology of the fungi, mycetozoa and bacteria . Plant morphology; Fungi; Myxomycetes; Bacteriology. CHAPTER VII.—PHENOMENA OF VEGETATION.—PARASITES. 361. spores; they appear in nature rather as epiphytic growths on the walls of cavities in the bodies of animals which are easily accessible from without, such as the passages of the ear and the bronchi. In most cases the spore of the parasite begins the emission of a germ-tube independently of the host, either after simple absorption of water or by appropriation at the same time of food-material produced outside the host. If the tubes or the hyphae which proceed from them then come into contact with the host, they fasten upon it in the way peculiar to each species. The most common case of the kind is when the spore finds its way by some mode of dissemination or other to the surface of the body of the plant or animal, and puts out germ-tubes which penetrate into the body. Parasites which, like Ancylistes Closterii and Polyphagus Euglaenae, attack unicellular organisms living in societies, send out mycelial branches from the individual first attacked, and these can fasten upon fresh individuals and by degrees on entire aggregates of the host-cells. Some facultative parasites of higher or- ^ ^ ganisms, Sclerotinia for example, Agaricus melleus and others of R. Hartig's tree-destroying species, behave in the same manner, since any of the hyphae or mycelial strands are able to make their way into new individual hosts. The act of penetration is accomplished in two ways; the germ-lube or branch of the myce- lium either grows into the interior of the host through a natural opening in it, or it pierces through the firm membranes of the surface of the body of the host. The one or the other mode is adopted according to the species and the kind of spore; it is seldom that both occur promiscuously. Many examples of the first kind are supplied by those endophytic parasites on plants, in which the germ

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