Moreover, there is one other fact which it is important to notice, viz., that there are substances which repel instead of attract the hyphæ. Is it not, then, asks Professor Ward, natural to conclude that the differences in behaviour of different parasites towards different host-plants, and towards the same host-plant under different conditions, probably depend on the chemotropic irritability of the hyphæ towards the substance formed in the cells on the other side of the membranous cell-walls? And when, as often happens, the effusion of substances, such as the cells contain, to the exterior is facilitated by over-distension and super-saturation, or by actual wounds, we cannot be surprised at the consequences when a fungus, hitherto unable to enter the plant, suddenly does so. To this proposition my answer is emphatically in the affirmative, since in my investigations into the “fungus-foot disease” (“_Mycetoma_”), 1871, of India, the entry of the fungus was in almost every case shown to be through an abrasion of the skin or a direct open wound; the majority of the cases reported were among the agricultural classes. When, then, as often happens, the effusion of substances, such as the cells contain, to the exterior is facilitated by over-distension and super-saturation, or by actual wounds, we cannot be surprised at the consequences when a fungus, hitherto unable to enter the plant, suddenly does so. Nevertheless, it must be admitted that the knowledge gained of parasites does not satisfactorily account for epidemic visitations over large areas. Habitat of Fungi and Moulds. [Illustration: Fig. 273.--Fungi and Moulds. Description of Figures.--_a._ Fungi Spores, taken in a sick chamber; _b._ _Aspergillus glaucus_; _c._ Yeast, recent state; _d._ Exhausted yeast, budding; _e._ Penicillium spores more highly magnified; _g._ Aerobic spores and mould mycelium; _h._ Aspergillus spore, grown on melon.] Habitat, Specialised Forms of Parasites.