Order. Taphrinaceæ. Of the genera belonging to this order, Taphrina, Endomyces, and Ascocorticium, the first is most important.
Endomyces decipiens is a parasite in the fruit-body of Armillaria mellea; E. magnusii lives in the gelatinous, fermenting exudations of Oak-trees; Ascocorticium albidum is found under the bark of the Fir-tree. Endomyces has chlamydospores and oidia.
The species of Taphrina are parasites, whose free asci may be found in great numbers, generally closely pressed together, on the parts of plants which they have attacked. The asci are developed directly from the ascogenous cells of a fertile, generally sub-cuticular, hypha, which arises from the sterile mycelium. The latter arises from the germinating ascospore, and may hibernate in the tissues of its host, particularly in the winter buds, and then with the commencement of the next period of vegetation it continues its growth side by side with that of its host. The hyphæ ramify in the intercellular spaces or beneath the cuticle, but have no haustoria. The ascospores (Fig. [105] A) and unripe asci may produce conidia.
Fig. 104.—Taphrina (Exoascus) pruni. Yeast-like budding of a germinating spore (× 600).
Fig. 105.—Taphrina betulina: a ascus filled with conidia; b germinating spores (× 600).
Very remarkable appearances, and swellings of the attacked tissues, are produced when the mycelium is perennial; for example, the “Witches’-brooms” and “Pockets.” The hard, hollow, stoneless plums, known as “Pocket” or “Bladder” Plums, are produced by considerable changes in the tissues of the fruit; these are caused particularly by T. pruni on several species of Prunus. The “Witches’-brooms,” on the contrary, are deformations of entire twigs or branches, and often attain a very large size. They occur on Alnus incana, caused by T. epiphylla; on Carpinus betulus, by T. carpini; on Cherry-trees, by T. cerasi; on Plum-trees, by T. insititiæ; on Birches, by T. turgida and T. betulina. T. deformans attacks the leaves of the Peach, and causes them to curl.
When a perennial mycelium is wanting, the infection is confined as a rule to white or yellow spots on the leaves, e.g. the commonest, T. sadebeckii, on Alnus glutinosa, and T. aurea on species of Populus. T. alni incanæ (Fig. [106]) causes considerable hypertrophies on the pistillate catkins of the Alder, which may be compared to the “pockets” of Prunus.
