hragmidium_, so that
this represents really a tricellular _Phragmidium_, linking the present
with the latter genus. In _Puccinia_ the number of species is by far the
most numerous; in this genus the spores are uniseptate, and, as in
all the _Pucciniaei_, the peduncles are permanent. There is great
variability in the compactness of the spores in the sori, or pulvinules.
In some species, the sori are so pulverulent that the spores are as
readily dispersed as in the Uredines, in others they are so compact as
to be separated from each other with great difficulty. As might be
anticipated, this has considerable effect on the contour of the spores,
which in pulverulent species are shorter, broader, and more ovate than
in the compact species. If a section of one of the more compact sori be
made, it will be seen that the majority of the spores are side by side,
nearly at the same level, their apices forming the external surface
of the sori, but it will not be unusual to observe smaller and
younger spores pushing up from the hymenial cells, between the
peduncles of the elder spores, leading to the inference that there is a
succession of spores produced in the same pulvinule. In _Podisoma_, a
rather anomalous genus, the septate spores are immersed in a
gelatinous stratum, and some authors have imagined that they have an
affinity with the Tremellini, but this affinity is more apparent than
real. The phenomena of germination, and their relations to _Roestelia_,
if substantiated, establish their claim to a position amongst the
_Pucciniaei_.[h] It seems to us that _Gymnosporangium_ does not differ
generically from _Podisoma_. In a recently-characterized species,
_Podisoma Ellisii_, the spores are bi-triseptate. This is, moreover,
peculiar from the great deficiency in the gelatinous element. In
another North American species, called _Gymnosporangium biseptatum_,
Ellis, which is distinctly gelatinous, there are similar biseptate
spores, but they are considerably broader and more obtuse. In other
described species they are uniseptate.

[Illustration: FIG. 22.--Pseudospores of _Puccinia_.]

USTILAGINEI.--These fungi are now usually treated as distinct from the
_Caeomacei_, to which they are closely related.[i] They are also
parasitic on growing plants, but the spores are usually black or
sooty, and never yellow or orange; on an average much smaller than in
the _Caeomacei_. In _Tilletia_, the spores are spherical and
reticulated, mixed w