MOULDS. 
201 
wet seasons. When the spring or summer is unusually dry, it is 
even difficult to meet with specimens for botanical purposes. 
Lettuce Mould. — A very similar mould (Peronosjpora gan- 
glioniformis) is sometimes very common in spring on the 
under surface of the leaves of the cultivated lettuce, appearing 
in definite white mouldy spots. By reference to the figure of 
a portion of a thread magnified (fig. 4), it will be seen that the 
peculiar form of the tips of the branchlets evidence the 
distinctness of this species. 
Tare Mould. — The under surface of the leaves of tares, 
and sometimes also of peas, are liable to attack from an allied 
species of mould ( Peronospora Vicice). In the spring of 1846 
it appeared amongst vetches in some districts to such an extent, 
as at one time to threaten the destruction of the crops ; but a 
succession of dry weather at once abridged its power and 
limited its mischief. Mouldy vetches and mouldy peas are, 
especially in moist seasons, evils to which the agriculturist 
knows his crops to be subject ; he may not know, however, 
that this kind of mould is of so near a kin to that which has 
acquired such wide-spread fame in connection with the potato 
(fig. 5) . Another species of fungus attacks the garden pea in 
damp seasons, forming small depressed brownish spots on the 
leaves and pods ; but this is quite distinct from the mould, 
though probably not less injurious. 
The Parsnip Mould (Peronospora macrospora ) is found on 
many umbelliferous plants ; but its attacks upon the parsnip 
are most to be deplored, because it . injures and ultimately 
destroys an article of human food. The plants infested with 
this parasite are first attacked in the leaves, but afterwards 
the roots become spotted and diseased in a similar manner to 
the potatos attacked by its congener. The disease has not 
hitherto been so general with the former as the latter ; but in 
some districts it has been far from uncommon. 
Spinach Mould. — -Spinach is likewise liable to suffer from 
the establishment of a mould upon the under surface of the 
leaves : unfortunately this is not unfrequent, and has been 
known in England certainly for the last fifty or sixty years, 
since it was figured by Sowerby in his “ British Fungi” as many 
years since. We have lately seen a bed of spinach utterly 
destroyed by this fungus ; whilst on another, not twenty yards 
apart, not a spotted leaf could be found. This mould is of a 
pale purplish-grey colour, and has large oval spores. It is the 
Peronospora effusa of botanists. 
Hitherto all the species of mould to which we have had 
occasion to refer have been found infesting plants more or less 
employed as food; but there remains one other species to 
which we must make special reference, and which affects one 
