308 PLANT LIFE. 



their foliage on the same place ; and it varies also 

 according to the dominant tree (Beech, Oak, or Pine), 

 and according to the amount of moisture. A study of 

 the same piece of woodland at different periods of the 

 years is, for this reason, full of interest. 



The assimilation-system of the wood is made up of 

 all these different floras. Any light which passes the 

 leaf-screen is sure to be intercepted by the undergrowth, 

 by lichens or mosses on the bark or by the ferns and 

 other plants on the floor. Thus the year's formation of 

 organic matter depends, not only upon the leaves of the 

 taller trees, but upon these other floras in addition. 

 Sooner or later pieces of old bark and twigs drop off 

 and the lichens and other Cryptogams are broken away 

 and join the mass of dead leaves, decaying mosses and 

 fern-fronds, petioles, etc., which covers the surface of the 

 ground. Along with these vegetable fragments, the 

 remains of insects and animals of all sorts, which have 

 found refuge in the wood, eventually reach the earth. 



All this organic matter is gradually made available 

 for further employment by the absorption system of the 

 wood. Therefore, it must be remembered that even the 

 lichens and mosses, and the minutest beetles that seek 

 refuge amongst them, assist in the nutrition of the 

 general plant community. 



The absorption system of the woods is exceedingly 

 complex. The dead leaves which fall in autumn are 

 very gradually disintegrated. The cork coat of the 

 twigs and branches requires a specially long period to 

 decay into plant food. It is only possible to mention 

 the most conspicuous stages, for very little seems to 

 have been published on this subject. Fallen leaves 

 appear to be first attacked either by insects, or by other 

 animals. These break their way through the cuticle 



