106 SAPROPHYTES IN WATER, ON THE BARK OF TREES, AND ON ROCKS. 



Often the trees only serve as supports, by means of which the plants in question 

 raise themselves out of darkness into light. Such food -salts as they require they 

 take, not from their support, but from the earth, into which they send absorptive 

 roots. As years go by, a quantity of inorganic dust collects in the forks of 

 branches and in the little rents and fissures in the bark of old trees, and this dust 

 gets mixed with crumbled particles of bark. The clefts, therefore, are more or 

 less full of vegetable mould, and this forms an excellent foster-soil for a large 

 number of plants. But it is not necessarily the case that all plants rooting in this 

 mould take up organic compounds from it. Thus, one finds not infrequently in the 

 angles of bifurcation of the trunks of old limes and other trees, little gooseberry 

 and elder bushes, and bitter-sweet plants, which have germinated there from fruits 

 brought by black-birds, thrushes, and other frugivora. These shrubs, in the forks 

 of limes and poplars hardly take any organic compounds from the mould in which 

 they are rooted, but confine themselves to the absorption of such mineral salts as 

 they may require. 



But, with the exception of instances of that kind, the great majority of plants, 

 nestling in the mould in crevices of bark, do take nutriment from this their 

 substratum in the form of organic compounds. In cold regions the plants living 

 in the mould of bark are for the most part mosses and liverworts. They cover 

 trunks and branches of old ashes, poplars, and oaks, with a thick green mantle, and 

 grow especially on the weather-side of the trees. In the tropics, on the other hand, 

 the fissured bark of trees is a rallying ground not only for delicate mosses and 

 moss-like Lycopodia, but also for a whole host of ferns and vivid flowering plants. 

 The number of small ferns which develop and unroll their fronds from chinks in 

 the bark of trees is so great that old trunks appear wrapped in a regular foliage of 

 fern-fronds. Of Phanerogams, in particular, the Aroidece, Orchidacece, BronieliacecB, 

 Borstenice Begoniacece, and even Cactacece (species of the genera Cereus and 

 Rhipsalis) bury their roots in the mould of bark. It is to be remarked that the 

 rosettes of Bromeliaceoe ornament chiefly the forks of trunks, whilst Dorstenice, 

 Orchidece, and the various species of Rhipsalis grow on the upper side of branches 

 that ramify horizontally; whilst, lastly, Aroidece and BegonicB take root, for the 

 most part, on the surfaces of huge erect trunks. 



Besides the mould collected in crevices and fissures of bark, the bark itself, that 

 is, the cortical layer, dead but not yet crumbled and mouldered into dust, forms 

 a nutrient substratum for a whole series of plants of most various affinity. 

 Many fungi and lichens penetrate deeply the compact bark, and their hyphal 

 filaments ramify between its dead cells. Other plants, instead of piercino- through 

 the substance of the bark, lay themselves flat upon its surface, and grow to it so 

 firmly that if one tries to lift them away from the substratum, either part of the 

 latter breaks off", or the adnate cell-strata are rent, but there is no separation of the 

 one from the other. If a tuft of moss (e.g. Orthotrichum fallax, 0. tenellum, or 

 0. pollens), growing on bark, or a liverwort {e.g. Frullania dilatata) closely 

 adherent to a similar basis, is forcibly removed, little fragments of the bark may be 



