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Scientific Memoirs by

fruit bodies are maturing, form no exception. The only difference is that,
whilst normally the new shoots are elongated, and bear large leaves, those
arising from an attacked shoot remain stunted, and put forth smaller leaves.
Now, it is a significant fact that these newly unfolded leaves, whether on healthy
shoots or not, although unfolded during the scattering of sporidia from the
neighbouring fruit bodies of Chrysomyxa, never present any outward sign
whatever of attack: they remain perfectly natural in appearance, though, as I
have already observed, those arising from infected stems are usually smaller
(Fig. 1, Plate I). This fact, of which I have convinced myself by repeated observ-
ation during the last three years, appears to render it extremely improbable
that the fungus is autœcious, and it is not therefore comparable with Chryso-
myxa Abietis. To this point I will, however, return. Another general point to
which I may draw attention before proceeding to a detailed description of the
fungus itself is that, although I have often searched for uredospores, I have
never found any trace of them.

A.—Microscopic Characters of Fungus.

      A.—On the Leaf-blade. —As already stated, localized affections of the leaf-
blade are not common. When found, they are always on the older leaves of the
preceding year's growth, and never on the newly unfolded leaves. In such
cases there is usually but one group of fruit bodies (about 25 in number on an
average) on the blade, distant from the midrib, and always on the lower surface.
The position is indicated above on the upper surface by a reddish-brown patch
of discolouration. The fruit bodies here are identical in shape and structure
with those on the petiole, but are a little smaller.

      The tissue of the leaf-blade is not much thickened at the sites of mycelial
invasion. Whilst the whole depth of tissue in the blade of a normal leaf is about
0.315 m.m., at attacked places it is about 0.346 m.m. The mycelium is,
however, very abundant in attacked areas, extending from midway between
the inner of the two palisade layers of cells, which normally exist in these leaves,
to the epidermis of the lower surface (Fig. 2, Plate II). The hyphæ, which
measure on an average 5µ in diameter, are of the usual characters, but contain
an abundance of orange-red oil globules; they ramify among the cells, sometimes
destroying them, but never in this place penetrating them to form haustoria.
The intercellular spaces in the spongy tissue are entirely filled up with myceli-
um. Indeed, in passing from natural tissue to the margin of attacked areas,
the first noticeable variation consists in the obliteration of these air spaces,
partly through their occupation by mycelium, and partly by cell proliferation
(Fig. 3, Plate II). Immediately below the young fruit bodies which have just
come to the surface, most of the spongy cells are disintegrated, but the palisade
cells remain normal in appearance. The first commencement (inception) of