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the changes of form which many fungi undergo in their progress 
to maturity ; at the same time that they are capable of propagating 
themselves while immature, in cases in which the conditions for 
attaining to a higher growth do not exist. Since the discoveries 
of Steenstrup respecting the alternation of generation among the 
lowest forms of animals, the same phenomenon has been observed 
among the lowest forms of vegetables; and it is now believed 
that there are whole tribes of fungi, hitherto considered distinct, 
which are but different phases of one another. 
The circumstances of the mildew fungus are as follows :-—It 
has been already stated that rust (Uredo rubigo, as it used to be 
called) and mildew (Puccinia graminis) are but two stages of the 
same plant, the former being an earlier form of the latter. This 
was clearly shown by the late Professor Henslow, in a paper 
published in the “Journal of the Royal Agricultural Society,” 
in 1841; and indeed the idea has been taken up that the Uredines 
generally, of which there are a great variety, are all of them but 
first phases of the Puccinewe—these two genera being in this way 
brought together. With regard to mildew, however,—the Puccinia 
graminis—it has been now further ascertained that this fungus, as 
it appears on wheat, does not ordinarily reproduce itself; but 
that, if the spores are sown on the leaves of the common berberry, 
they give rise to the well-known orange-coloured spots of Acidium 
berberidis, formerly considered as a fungus belonging to an entirely 
different group. The spores of the Acidiwm, on the other hand, 
do not reproduce the Acidium, but the Puccinia in its rust form, 
showing the berberry fungus to be the third and last of a series 
of changes through which one and the same species passes before 
arriving at maturity ; and so explaining how the proximity of a 
berberry bush, where it exists, may cause mildew in wheat. But 
a seeming difficulty here presents itself: if the berberry fungus is 
the same as the mildew fungus, and the form which the latter 
finally assumes—supposing the conditions favourable—how do we 
explain the extremely common cases in which the wheat is still 
