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POPULAR SCIENCE REVIEW. 
covered beneath with the bright orange- coloured dust. This 
is the coltsfoot rust (Goleosjperium Tussilaginis , Lev., Plate XII. 
fig. 28), which may serve as a type of the rest. It may be 
observed that a species of cluster-cup, or CEcidium , with 
spores of nearly the same colour, is also to be found on the 
leaves of the same plant ; but in this case the upper surface of 
the leaf has also corresponding purplish spots, and, what is of 
still more importance, the spores are seated in small fringed 
cups. The rust is common till the wintry frosts have set in, 
and is far more conspicuous than the cluster-cups. A kind of 
di-morphism prevails in all the species of this genus. Some 
of the pustules resolve themselves into a kind of powder, 
whilst others remain entire and solid. Generally there is the 
largest proportion of globose, dust-like, free spores, produced 
in the earliest developed fungi, whilst they become more rare 
towards the close of the season. The permanent spore-spots 
consist of obovate cellules placed side by side, each of which 
is divided transversely by three or four septa, and is filled 
with an orange-red endochrome (Plate XII. fig. 29) ; the 
exterior being enveloped in a kind of mucous layer. The 
arrangement of spores when packed together in the pustule 
is shown in Plate XII. fig. 30, from an allied species. When 
these spores germinate, which they do with great readiness, 
each division emits a long tube, which generally remains 
simple and undivided, and from its extremity is produced 
a reproductive body of an obovate or nearly kidney-shape. 
These filaments are about -rioth of an inch in length, of a 
colourless transparent membrane, along which the orange-red 
contents of the spores pass into the newly-formed sporidia, or 
reproductive bodies by which they are terminated. Most of 
these reniform sporidia disengage themselves from the fila- 
ments on which they are produced, and either elongate 
themselves into a simple and uniform filament, or swell at the 
extremity as if to reproduce a second spore. If the newly- 
formed sporidia do not become free, they increase the length 
of their primitive filament, which by a frequent repetition of 
the process becomes a tube swelling out at unequal distances. 
The summer spores, or pulverulent spores of the first gene- 
ration, which are analogous to the Uredo-spores of Aregma, 
are also capable of germination, for, if placed in favourable 
circumstances, they will develop very long filiform processes, 
which either remain simple or become more or less branched, 
but always nearly uniform in their diameter. M. Tulasne 
states that he has observed this germination many times, 
though we have been less fortunate. 
Of the six species of this genus known to occur in Great 
Britain, the majority may be commonly met with. That very 
