On a Chrysomyxa on Rhododendron arboreum, SM.

(CHRYSOMYXA HIMALENSE, NOV. SP.)

BY

SURGEON-MAJOR A. BARCLAY, M.B.

BENGAL MEDICAL SERVICE.

    This is an extremely conspicuous, and very widely distributed Uredine in
the Simla region, where Rhododendron arboreum is most common. The
mycelium is, for the most part, perennial, and attacked shoots are, year after
year, so arrested in growth that a conspicuous clump of leaves ("witches'
broom" or "Hexenbesen") is produced, by which attacked trees are readily
distinguished at any time of the year. Were it not for this the presence of
the parasite in any tree would be recognizable only from early spring to the end
of May, during which time the remarkably striking fructification has com-
menced and ended. This has its seat especially on the petioles, and along the
midrib a short distance into the leaf blade. When ripe, the fruit bodies clothe
the petioles so densely as to hide it completely (Fig. 2, Plate I). Each separate
fruit body is very prominently club-shaped, or mushroom-shaped. The ex-
panded upper part measures on an average 2 m.m. in diameter, and the whole
body about 1.5 m.m. in length from its base on the petiole. Some are, of
course, a little larger and some smaller. But, although the fruit bodies are
characteristically situated on the petioles and on the lower portions of the
midribs, they are also occasionally found on the main axis of the shoot (Fig. 1,
Plate I), and as isolated groups on the leaf blade. During dry weather, or if
they be kept a few hours in a moist atmosphere, they become pure yellow, due
to rapid sporidial formation. This change in colour is very striking.

    Very early in spring (March) the petioles of the leaves which were
unfolded in the previous spring, but which are usually much smaller in size than
normal leaves on healthy shoots, are seen to be uniformly orange red, while as
yet there is no swelling or distortion of any kind. Although smaller, the leaves
are not in any other respect different from normal leaves. Later, small wart-
like projections are formed on the petioles, and these grow gradually until,
towards the latter part of April and early May, they attain their maximum
size and shape. While this maturation of the fruit bodies is proceeding,
the Rhododendron trees are putting forth their new shoots and leaves, and
the shoots which are invaded by the parasite, and on whose old leaves the