Ascomycetes with FREE ASCI; sometimes also conidia, chlamydospores and
oidia. One order.
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.
[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).]