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. [Illustration: FIG. 104.--_Taphrina_ (_Exoascus_) _pruni_. Yeast-like budding of a germinating spore (× 600).] [Illustration: 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_. [Illustration: FIG. 106.--_Taphrina alni incanæ_ on the Alder (nat. size).] Series 2. =Carpoasci.= The Carpoasci are Ascomycetes, whose asci are enclosed in fruit-bodies, _i.e. ascocarps_. The accessory means of reproduction are free conidiophores (Fig. 109), conidial-layers (Fig. 122), conidiocarps (Fig. 120 _D_, _E_, etc.), chlamydospores and oidia. For the different methods of distributing the ascospores, see p. 92.