Fig. 96.—Entyloma ranunculi. 1. Cross section of a portion of a leaf of Ficaria permeated by the mycelium; a bundle of hyphæ with conidia emerging from a stoma; in one of the cells are found four brand-spores. 2. A brand-spore developed in the middle of a hypha.
It most frequently happens that the germ-tube enters the host-plant at its most tender age, that is, during the germination of the seed; the mycelium then wanders about in the tissues of the shoot during its growth, until it reaches that part of the plant where the spores are to be formed. The spore-formation takes place in the same way in all those species whose brand-spores are developed in the floral parts of the host-plant. Many Brand-Fungi have, however, a more local occurrence, and the mycelium is restricted to a smaller area of the leaf or stem. Those organs of the host-plant in which the brand-spores are developed often become strongly hypertrophied. In perennial plants the mycelium winters very often in the rhizome.
Fig. 97.—Doassansia alismatis. 1. A fruit-body, formed by a covering of oblong hyphæ, which encloses a mass of brand-spores, and is embedded in the leaf-tissue of the host-plant; 20 times natural size. 2. A germinating brand-spore, 500 times natural size. 3. Three connected resting-spores, 400 times natural size. 4. Two conidia grown together, 600 times natural size.
The brand-spores are the winter resting-spores of the Brand-Fungi. They arise in the tissues of the host-plant, which is often destroyed, and become free through the rupture of the epidermis; they are thick-walled, generally brown or violet, and very often possess warts, spines, or reticulate markings. Fruit-bodies, that is enclosed organs of reproduction, are found in few genera (Sphacelotheca, Graphiola; Doassansia, Fig. [97]). In Tolyposporium, Tuburcinia, Thecaphora (Fig. [102]), etc., the brand-spores are united into a ball of spores. On germination the brand-spores behave as chlamydospores, namely, as the fundament of conidiophores, by emitting a short germ-tube, i.e. a conidiophore (“promycelium”). The Ustilaginaceæ (Fig. [99], 2) have a short transversely divided conidiophore, with laterally developed conidia (comp. the basidia of the Protobasidiomycetes). The conidiophores of the Tilletiaceæ are undivided (unicellular promycelia), and bear the conidia terminally, and so resemble the basidia of the Autobasidiomycetes.
Fig. 98.—Tuburcinia. 1. T. trientalis. Hyphæ, some of which bear conidia at the apex, forcing themselves out between the epidermal cells on the under side of the leaf; 320 times natural size. 2. T. trientalis. A ball of spores in which some of the individual brand-spores are about to germinate; 520 times natural size. 3. T. primulicola: various forms of conidia (500 times natural size).
In Tilletia, Entyloma, Neovossia, Tuburcinia, the brand-spores germinate and form basidia-like conidiophores with spindle-shaped conidia; their mycelium, on the other hand, produces later only single, sickle-shaped conidia, so that two kinds of conidia are found, as in a few Basidiomycetes. In some species, e.g. Ustilago hordei, the brand-spores only germinate vegetatively and form a mycelium. In nutritive solutions (solutions of dung, etc.) where they live as saprophytes, the brand-spores of many species emit germ-tubes, and on these, yeast-like conidia are produced by repeated budding, which grow into mycelia only when the nutritive solution is exhausted. These conidia have not the power of producing alcoholic fermentation. The very numerous conidia, which are found in the dung of herbivorous animals, are probably the yeast-conidia of Brand-Fungi. The brand-spores, which are eaten by animals with the grain and hay, pass into the dung and without doubt give rise to a very rich multiplication of yeast-conidia.
