SAPROPHYTES IN THE HUMUS OF WOODS, MEADOWS, AND MOORS, 109 
and plants with foliage, flowers, and fruit of a form adaptable to cracks and holes 
are able to establish themselves in the mould there, just as well as in that collected 
in crevices of bark. In one respect, indeed, they are even more favourably situated. 
For the humus in bark gets quite dry in long periods of drought, because no water 
is yielded to the bark by the wood of a tree, even though the latter be abundantly 
supplied with sap; whereas, in the case of rocks the probability is, the clefts being 
very deep, that even when the top layers of humus filling them yield up their water 
to the air, a certain restitution of moisture takes place from the deeper parts, which 
are never quite dry. Moreover, plants growing in the mould of rock crevices are 
able to send their roots down to much deeper strata than is possible in the case of 
bark. This is another reason why deep cracks in rocks, filled with humus, exhibit 
a richer flora, as a rule, than do the much shallower crevices in the bark of trees, 
although, as has been said before, the two habitats have many plants i1 common. 
It is more difficult to explain how it happens that plants which derive their 
sustenance, not from the mould in crevices, but from the substance of the bark 
itself, and which lie flat against its surface, are also found adhering to walls of 
rock. As an example take Frullania tamarisci, a Liverwort with small brown 
bifurcating stems, which bear double rows of leaves and are of dendritic appearance. 
This plant grows equally well on the bark of pines or on the face of adjacent gneiss 
rocks. At first sight it would seem scarcely possible that a plant of this kind, 
clinging to the unfissured surface of rock, should be in a position to obtain organie 
compounds from its substratum. This is nevertheless the case. Closer inspection 
reveals the fact that the Liverwort does not adhere to blank rock, but to a part 
formerly clothed by rock-lichens. This inconspicuous incrustation of dead lichens 
is a complete substitute for the superficial layer of bark, and it is into it that the 
Frullania tamarisei sinks its roots. Another way by which food is supplied to 
plants adherent, like the above, to vertical and unfissured rocks will be discussed 
later on. 
SAPROPHYTES IN THE HUMUS OF WOODS, MEADOWS, AND MOORS. 
Damp shady woods, especially pine woods, are particularly well furnished with 
saprophytes. Here again we find representatives of the same families as choose the 
bark of trees for their habitat. On the ground of woods, the most characteristic 
forms are mosses, fungi, lycopods, ferns, aroids, and orchids. ‘The dark-brown 
humus, produced from dropped and decaying needles, is first of all covered by a 
rich carpet of mosses, such as the widely distributed Hylocomiwm splendens, 
Hypnum triquetrum, and Hypnum Crista-castrensis. The mouldered dust of 
dead trees has a clothing of Tetraphis pellucida and of Webera nutans, and 
decaying trunks are overgrown by the cushions of species of Dicranum (Dicranum 
scoparium, D. congestum, Dicranodontium longirostre), pale feathery mosses 
(Hypnum uncinatum and H. reptile) and various liverworts. Everywhere above 
the soft, ever-moist carpet of moss rise green fronds belonging to broad-leaved ferns. 
