On Wlieat Mildezo. 
497 
barberry, as if it were the cause of mildew in wheat. Great, 
however, as are the changes which fungi undergo occasionally in 
passing from one condition to another, there is not the slightest 
reason for imagining that the j^cidium is a transitorial state of 
Avheat-mildew. It has its own mode of propagation, and passes 
through nearly the same phases of vegetation as the mildew, 
without affording a suspicion that it is not a perfect plant. The 
whole story has no doubt arisen from the ^cidium being 
common on the barberry in hedges surrounding wheat-fields ; 
and there is reason to believe the report is true, that wheat has 
been especially mildewed in the neighbourhood of the j^cidium. 
The peculiar situation may, however, be equally favourable to 
either parasite ; and it is to be observed that mildew is pecu- 
liarly prevalent in districts where the barberry is unknown 
•except as a garden plant." 
The careful investigations and experiments of De Bary, 
corroborated by the subsequent discovery by other botanists of 
similar phenomena in the life-history of other fungi than 
mildew of wheat, have, however, determined beyond all question 
that the j^cidium of the barberry, the rust and the mildew of 
wheat, are only stages in the life of the same plant, though each 
stage presents the phenomena we have been accustomed to con- 
sider characteristic of a perfect plant by producing innumerable 
spores or seeds capable of giving rise to new individuals. De 
Bary has indeed produced each stage of the plant from the spores 
produced by the previous stage. 
Let us now trace the history of the fungus through its different 
forms of life. 
The first stages in its life, after the rest of the winter, is that 
which it passes on the barberry. In the spring the leaves of 
this plant may sometimes be found 
with swollen yellowish spots, which in ^^S- l-Single Cup of a 
a short time burst through the skin, ^^aL^-^Leaf 
and form little bordered cups filled ^ 
with a reddish powder. Under this 
form the plant is known as ^cidium 
herberidis. The genus yT^cidium was, 
till recently, believed to contain a 
clearly limited aiid natural group of 
species, of which nearly forty were 
found in Britain on the leaves or 
stems of the barberry, gooseberry, 
buttercup, anemone, spurge, nettle, &c. 
That on the barberry occurs chiefly on the leaves, but some- 
times attacks the leaf-stalk and the fruit. It may be detected 
in May or June as a bright red spot on the under side of the 
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