ith delicate threads, from whence they spring. In
the best known species, _Tilletia caries_, they constitute the "bunt"
of wheat. The peculiarities of germination will be alluded to
hereafter. In _Ustilago_, the minute sooty spores are developed either
on delicate threads or in compacted cells, arising first from a sort
of semi-gelatinous, grumous stroma. It is very difficult to detect any
threads associated with the spores. The species attack the flowers and
anthers of composite and polygonaceous plants, the leaves, culms, and
germen of grasses, &c., and are popularly known as "smuts." In
_Urocystis_ and _Thecaphora_, the spores are united together into
sub-globose bodies, forming a kind of compound spore. In some species
of _Urocystis_, the union which subsists between them is comparatively
slight. In _Thecaphora_, on the contrary, the complex spore, or
agglomeration of spores, is compact, being at first apparently
enclosed in a delicate cyst. In _Tuburcinia_, the minute cells are
compacted into a hollow sphere, having lacunae communicating with the
interior, and often exhibiting the remains of a pedicel.

[Illustration: FIG. 23.--_Thecaphora hyalina._]

[Illustration: FIG. 24.--_AEcidium Berberidis._]

AECIDIACEI.--This group differs from the foregoing three groups
prominently in the presence of a cellular peridium, which encloses
the spores; hence some mycologists have not hesitated to propose
their association with the Gasteromycetes, although every other
feature in their structure seems to indicate a close affinity
with the _Caeomacei_. The pretty cups in the genus _AEcidium_ are
sometimes scattered and sometimes collected in clusters, either with
spermogonia in the centre or on the opposite surface. The cups
are usually white, composed of regularly arranged bordered cells
at length bursting at the apex, with the margins turned back and
split into radiating teeth. The spores are commonly of a bright
orange or golden yellow, sometimes white or brownish, and are
produced in chains, or moniliform strings, slightly attached to
each other,[j] and breaking off at the summit at the same time that
they continue to be produced at the base, so that for some time
there is a successive production of spores. The spermogonia are
not always readily detected, as they are much smaller than the
peridia, and sometimes precede them. The spermatia are expelled
from the lacerated and fringed apices, and are very minute and
colourle