208 Keegan: The Birch Tree. 
(silica, lime, or magnesia salts) in the old organ. With respect 
to the wood there are tndications of a rapid growth of all the 
tissues simultaneously with defective differentiation. For in- 
stance, in May and June, z.e. the period of great vegetative 
activity, the outer wood-rings of the stem and branches. are 
almost devoid of starch, ze. there is only a feeble reserve of 
starch in the wood, the vessels are still free and open for the 
circulation of sap, and the amount of tannin produced is very 
small, so that everything forbids the differentiation of the 
wood elements into alburnum and duramen. In the region 
of the bark, moreover, the rapid growth and so far perfect 
vegetation lead the way to a subsequent inanition, whereby 
a powerful periderm is constructed. The pressure of the 
actively growing internal tissues rends the epidermis, imparts a 
potent stimulus to the phellogen (cork-cambium), and the 
attractive phenomenon of the silver-barked Birch is the result. 
The production of tannin being, however, comparatively poor, 
the outer bark. is white, and not brown, as in most other 
instances. 
But whereas the vegetation so far as the foliar organs are 
concerned, is comparatively perfect and unexhausted, the 
chemical development, so to speak, of the tree is decidedly 
backward. Thus the young leaves produce a not insignificant 
quantity of volatile oil, resin, and tannoid, while, nevertheless, 
in the old organs the amount of tannin and phloroglucin is 
distinctly insignificant. The mature bark contains only some 
5 per cent. of tannin and only a trifling indication of free phloro- 
glucin. Thus it appears that the process of deassimilation is 
very incomplete, and stands in this respect in marked contrast 
to that of the nearest ally, vzz. the Alder. In fact, this is the 
chief reason of the comparatively short life of the Birch tree, 
vis. some 110 years. The wood never becomes perfect, no true 
duramen is formed ; indeed, when cut and exposed to the air, 
it putrifies very rapidly and completely owing to a serious 
poverty in tannin and resin. The copious ‘ bleeding’ in spring 
is dependent on a portion of the crude sap, taken up by the 
roots, being pressed into the mature air-containing vessels, 
which (as aforesaid), although mature, are nevertheless so free 
from the thickening and incrusting substances ordinarily charac- 
teristic of ‘perfect’ wood, that the circulating sap (the spring 
maximum of starch production in the wood having ‘been 
attained), readily finds a place of rest, so to speak, on its 
passage upwards, and from whence it may be ioe withdrawn 
by the simple process of tapping. 
Naturalist, —~ 
