188 ROSS: PTILIDIUM PULCHERRIMUM (WEB), HAMPE.
ground to about 6 feet up the trunk. Also growing on the tree
are some lichens, two mosses, Dicranum scoparium and one of the
Hypnaceae, and the hepatic Lophocolea heterophylla. Lichens,
mosses, and L. heterophylla appear amongst the Ptilidium,
even when at first sight this seems to be growing in dense patches.
In places, the lichens are in possession. The Dicranum is in
tufts, as well as scattered ; and, at the foot of the tree, the
Lophocolea has established itself. The tree is evidently a favour-
able situation, and there is some competition for sites on its bark.
From the area of the trunk on which the Ptilidium is found
and from the amount of old plant some of the clumps show, one
concludes that it has been there some time. A somewhat
remarkable feature is the ease with which patches of the
Ptilidium can be lifted from the tree trunk, especially where
it grows most densely. Last summer, a long branch of a field
rose reached the tree ; and, in high winds, this may have been
forced across the trunk and may have scratched off hepatic,
moss, and lichen. Pieces of Ptilidium were found on the ground,
but these may have been washed off by heavy rains. The
branch of the fieldrose is no longer there to do damage ; but, after
the recent thaw, six or seven pieces of hepatic and moss, chiefly
Ptilidium, were found on the ground near the base of the tree,
and three pieces of Ptilidium were hanging precariously, clearly
the work of the melting or slipping snow. At first, one con-
cluded from the depth of the patches that new plants of Ptilidium
had grown upon old ones, or that the older parts of
the plants had died and the hold on the tree trunk
had loosened. This may be so in some instances, but
the examination of a patch of plants in the course of
preparation for preservation revealed that the Ptilidium
had overgrown the Hypnum. It would also seem able
to spread its way into a tuft of plants of Dicranum. Lichen
seems apt, on the other hand, to establish colonies amongst the
Ptilidium. As already stated, Lophocolea heterophylla holds
sway at the foot of the tree ; and, in preparing Ptilidium for
the collection, one was rather surprised to find, amongst a patch
of Ptilidium plants, young and healthy plants of L. heterophylla.
These plants were frequently growing underneath, rather than
at the top level of, the Ptilidium, and now and then forced their
way through and showed on the surface of the Ptilidium growth.