56 P. Q. KEEGAN [ JULY 



reserve is feeble and readily exhausted. So far they agree, but in the 

 Birch the process of de-assimilation is not so complete as that in the 

 Alder. In the former it is not pushed much beyond the lavish pro- 

 duction of colourless waxes, resins, and volatile oils, and hence the 

 outcome of the tannins, phlobaphenes, pigments, etc., is considerably 

 restricted. The result is, that in the " queen of the woods " we have 

 a silvery whitish bark with about 30 per cent white resin (betulin) 

 approaching a wax or camphor in character, and only about 5 per cent 

 tannin (all too feeble to impart a crimson coloration to the autumn 

 leaves), together with an amount of phlobaphene too small to over- 

 power the predominant suberification. The bast of this tree exhibits 

 considerable lignification, but it is clear that the phellogen is perhaps 

 the most active formative tissue in the entire rind. The case is pretty 

 much reversed in the marsh-loving Alder wherein de-assimilation seems 

 to reach its highest intensity. The bark of this tree sometimes con- 

 tains as much as 2 per cent of a tannin which is highly carbonaceous, 

 and very readily forms high red-brown and muddy shaded anhydrides 

 of an eminently antiseptic character. The tannin penetrates freely 

 into the medullary rays, parenchyma, and pith of the wood (it is very 

 sparse in birch wood) ; in fact, without a doubt the Alder, taken all 

 in all, is by far the most richly tannin-bearing of all our forest trees, 

 and this constituent is of such a character and composition that it 

 subserves the purpose of lignification rather than of embellishment, for 

 as a chromogen it is useless save for colours dark and dun. The leaves 

 contain a darkish brown oily matter, while the bark of the twigs 

 encloses a bright yellow pasty mass of fat, wax, and a trace of volatile 

 oil ; carotin is very scarce even in the leaves. Cells filled with a 

 homogeneous phlobaphenic matter seem mostly to replace or represent 

 the highly suberified periderm of its congener the Birch. 



The members of the sub-order Cupuliferae, viz. the Oak, Spanish 

 Chestnut, and Beech, are more closely allied in chemical respects 

 than the two foregoing species. No member of the vegetable 

 kingdom has been more thoroughly and exhaustively investigated 

 than the Oak. The peculiar shape of its leaves is no pledge of 

 their physiological faculty, which is extremely powerful. The 

 amount of starch which this tree produces and stores up (there is 

 37 per cent in the acorns) is, I think, considerably greater than that 

 of any tree in our woods. A very distinctive variation is, however, 

 observable in the Beech, where even in January and February the wood 

 is very rich both in oil and starch, every cell of the parenchyma in the 

 outer rings being full of the latter (which is not the case in most starch 

 trees), and this predominance continues up till April when the wood is 

 found still to be rich in oil (in fat-trees generally there is little oil in 

 spring or summer). In fact, the Beech, chemically speaking, is a 

 peculiarly eccentric organism. Even in its most massively developed 

 trunk there is no marked distinction between the heart-wood and the 



