284 PAULSON : NOTES ON THE ECOLOGY OF LICHENS.
Cladonia macilenta, podetium, on cone of P. sylvestris, in
one year 1.0 cm.
Cladonia fimbriata, podetium, on cone of P. sylvestris, in one
year, 0.7 cm.
C. fimbriata, on rabbit pellets, podetium, measured 0.5 cm.
C. Flaerkiana, on rabbit pellets, podetium (fig. 2), fertile,
measured 0.7 cm.
C. macilenta, on rabbit pellets, podetium (fig. 2), fertile,
measured 0.6 cm.
These lichens were all quite small when they first came under
observation. Those growing on rabbit pellets presented a diffi-
culty, as it was necessary to estimate the length of time that a
pellet remains whole and spherical in form. The effects of
rain and frost, and the result of the action of bacteria, lead to
the assumption that growth begins upon the pellets before they
are exposed to wintry weather. Lichens, such as those named
above, together with Lecidea granulosa Schoer., are quite abun-
dant and fertile on rabbit pellets on heathlands in the early
spring months. The growth of a lichen thallus, such as that of a
Cladonia, upon a pellet (fig. 2) protects it from the disintegrating
effect of winter ram and frost. Fertile species of Cladonia and
Lecanora varia are frequently found on cones of Scotch fir and
larch—on the latter, before they fall from the tree. Xanthoria
(Physia) parietina Th. Fr. is frequently found on the bones of
sheep that lie scattered over the South Downs (fig. 1 facing
p. 257). This lichen on the bones has been found to measure
across the widest diameter from 2, to 3 mm. up to 50 mm.,
and is frequently covered with well-developed apothecia. We
cannot, of course, tell the exact age of these plants, but the
fact that they are there and are fertile, is sufficient to show
that a long period of growth is not required before apothecia
are produced.
The rapid development of two extensive patches of terricolous
lichens, one of Lecidea uliginosa and the other of Baeomyces
roseus, already mentioned on a previous page, Were the result
in each case of the coalescence of a large number of plants
that commenced growth at many separate centres on the same
patch of bare ground. As the lichens grew and came into
contact with each other such complete fusion took place that
individuality was lost in the formation of a mat-like structure