CLUSTER-CUPS. 
20 
The leaves of pear-trees afford a second species of this 
genus sufficiently distinct to commend it to our notice. 
Sometimes it is very common, at others but few examples are 
to be met with. The clusters occur on the under-surface, 
and consist of half a dozen or less of large peridia, pointed at 
the apex and swelling in the middle so as to become urn- 
shaped. These vessels or thecae split into numerous threads 
or laciniae, which remain united together at the apex. Like 
the species already noticed, this is brown and inconspicuous 
except on account of its size, for it is the largest of all that 
we have had occasion to notice. 
The third species occurs on the under- surface of the leaves 
of the mountain-ash. The peridia are clustered on a rusty 
orange-coloured spot which is visible on the upper surface. 
They are long and cylindrical, with an evident tendency to 
curvature, the mouth is serrated, but not split up into threads, 
as in the species found on the hawthorn. The peridia are 
often abortive, and nothing is to be seen but the rusty 
thickened spot on the leaf. The clusters and spores are of 
a brighter reddish brown than in either of the other species. 
All are remarkably distinct, and perhaps the most curious 
and interesting of any that we have passed in review. To 
botanists the species found on the hawthorn is known as 
Rcestelia lacerata, that on pear-leaves as Rcestelia cancellata, 
and the one on the leaves of the mountain-ash as Rcestelia 
cor nut a. 
Dr. Withering observed the spore-spots on the leaves of 
the mountain-ash, but was evidently puzzled to account for 
them. He writes (in his Arrangement of British Plants), “ The 
spots on the leaves of Sorbus aucujparia consist of minute 
globules intermixed with wool-like fibres. On examining 
many of them in different states, I at length found a small 
maggot in some of the younger spots, so that the globules are 
probably its excrement, and the fibres, the woody fibres of 
the plant unfit for its food.'” 
Only two species of cluster-cups are described in Withering's 
Flora under the genus Lycojoerdon : one of these is now 
called JEcidium comjpo sit arum , and is found on various com- 
posite plants ; the other includes the species found on the 
wood-anemone and that on the moschatel, and also probably 
a species of Puecinia on the wood-betony. 
To render our paper more complete, though of less import- 
ance to the microscopist, we may allude to the other two genera 
comprised within this order. Peridermium is the name of 
one genus which contains two British species found on the 
leaves and young shoots of coniferous trees. In this genus the 
peridium bursts irregularly, and does not form cups or horns 
