,
have had their relations to certain species of _Sphaeria_ indicated,
and these are no longer regarded so much as species of _Hendersonia_
or _Diplodia_ as the pycnidia of _Sphaeria_. Other and more minute
perithecia, containing minute, slender stylospores in great numbers,
formerly classed with _Aposphaeria_, _Phoma_, &c., but are now
recognized as spermogonia containing the spermatia of _Sphaeriae_. How
these influence each other, when and under what circumstances the
spermatia are instrumental in impregnation of the sporidia, is still
matter of mystery. It is clear, however, that in all these conidia,
macrospores, microspores, and some spermatia, or by whatever names
they may be called, there exists a power of germination. Tulasne has
indicated in some instances five or six forms of fruit as belonging to
one fungus, of which the highest and most perfect condition is a
species of _Sphaeria_.

[Illustration: FIG. 36.--_Uncinula adunca._]

PERISPORIACEI.--Except in the perithecia rupturing irregularly, and
not dehiscing by a pore, some of the genera in this group differ
little in structure from the _Sphaeriacei_. On the other hand, the
_Erysiphei_ present important and very interesting features. They
occur chiefly on the green parts of growing plants. At first there is
a more or less profuse white mycelium.[AC] This gives rise to chains
of conidia (_Oidium_), and afterwards small sphaeroid projections
appear at certain points on the mycelium. These enlarge, take an
orange colour, ultimately passing into brown, and then nearly black.
Externally these perithecia are usually furnished with long,
spreading, intertwined, or branching appendages, sometimes beautifully
branched or hooked at their tips. In the interior of the receptacles,
pear-shaped or ovate asci are formed in clusters, attached together at
the base, and containing two or more hyaline sporidia. Other forms of
fruit have also been observed on the same mycelium. In an exotic
genus, _Meliola_, the fulcra, or appendages, as well as the mycelium,
are black, otherwise it is very analogous to such a genus of
_Erysiphei_ as _Microsphaeria_. In _Chaetomium_, the perithecia bristle
with rigid, dark-coloured hairs, and the sporidia are coloured. Our
limits, however, will not permit of further elucidation of the complex
and varied structure to be found amongst fungi.[AD]

[A] A curious case occurred some years since at Bury St. Edmunds,
which may be mention