MOULDS. 
199 
times solitary, at others in pairs or strung together like beads 
for a necklace. Amongst all this variety of arrangement there 
is order, for these are but features or partly the features of the 
different genera of which the Mucedines are composed. One 
of the genera is termed Peronosporci, and to this the parasitic 
fungus of the potato, and some others to which we shall have 
occasion to refer, belongs. In this genus the threads are 
generally branched but without articulations. The spores, or 
seed-like bodies, are of two kinds ; one kind is borne on the 
tips of the branches ; and the other kind, which is larger and 
globose, is borne upon the creeping mycelium or spawn. All 
the members of this genus with which we are acquainted are 
parasitic on living plants, inducing in them speedy decay, but 
preceding that decay of which they are themselves the cause. 
Hence we have deemed it the more advantageous course both 
for writer and reader to associate together the different species 
of this particular genus of parasitic moulds in the same paper, 
rather than bring together the different kinds of Fungi, belong- 
ing perhaps to widely separated genera, but all associated 
with, or parasitic upon, the same plant. The botanical student 
will thank us for following this plan, and the general reader 
will labour under no disadvantage, in this instance at least, 
from the similarity of the diseases produced in the plants 
infested. 
The potato mould has been judiciously named Peronospora 
infestans, or, as it was at first called, Botrytis infestans ; but 
on a revision of the genera Botrytis and Peronospora , it was 
transferred to the latter genus, in which it remains. Three 
names were given to it, within a short period of each other, by 
different mycologists, in ignorance of its having already re- 
ceived a name. The one we have adopted appears to have 
the priority, at least of publication, and was given by Dr. 
Montagne. That of Botrytis devastatrix was given by Madame 
Libert, and Botrytis fcdlax by M. Desmazieres. The principal 
feature in this species seems to consist in the branches be- 
coming alternately thickened and constricted, so as to resemble 
a moniliform string, or necklace of little bladders or vesicles. 
The branches are also more erect than in the allied species, 
and the spores are solitary on the tips or from the sides of the 
branches, and not in pairs or clusters, and the tips are simple, 
and not bifid or trifid, as in most of its allies. It need scarcely 
be remarked, that a high power of the microscope is necessary 
to make out the distinctive features of the different members 
of this genus, and that to the naked eye they only appear as a 
minute whitish mould. As already stated, this little fungus 
makes its first appearance on the under surface of the leaves, 
especially the lower ones, of the potato plant, and afterwards 
