SAPROPHYTES IN THE HUMUS OF WOODS, MEA.DOWS, 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 

 m 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 in common. 



It is more difiicult 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 organic 

 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 tamarisci 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 MOOES. 



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 Hylocomium spiendens, 

 Hypnwm triquetruon, and Rypnum 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 Dici'anum (Dicranum 

 scoparium, D. congestum, Dicranodontium longirostre), pale feathery mosses 

 {Hypnum uncinatum and R. reptile) and various liverworts. Everywhere above 

 the soft, ever-moist carpet of moss rise green fronds belonging to broad-leaved ferns. 



