THE CHEMISTRY OF THE FOREST. 



By P. Q. KEEGAN, LL.D. 



By the chemistry of trees is meant the detection by analysis 

 of such separable and distinctive organic and inorganic bodies 

 as are incidental to the vital processes thereof, whether these 

 substances are the direct outcome of the arboreal life energy, 

 or are merely the by- or waste-products of the spent and 

 exhausted activities. The tree, indeed, may be regarded as 

 the outward and visible sign of an inward and wholly 

 invisible force. The capital force is the one called " vital," 

 shrouded in mystery ; but chemical forces, aided in some 

 cases by physical forces, are created and set a-going thereby, 

 and are manifested in visible and tangible shape by the 

 inevitable consequences of a production of principles mostly 

 not detectable in the animal or mineral kingdom. It must 

 be admitted, indeed, that several of the most distinctive 

 constituents of the body of the tree, its stem, leaf, and flower, 

 are not the results of any chemical processes known to science, 

 and cannot be artificially reproduced by the most skilful 

 application of the most modern and approved synthetic 

 methods and expedients; that is to say, the chemical origin 

 of what are called the products of vegetable assimilation is a 

 mystery shrouded beneath the inscrutable veil of forest 

 secrecy. With regard to the woodland soil, it may be briefly 

 stated that it contains much humus, i.e., it is highly charged 

 with organic matter, which is the essential condition of the 

 life of certain fungi which assimilate the nitrogen and carbon 

 thereof, and by association with the roots of the tree 

 (mycorhiza), contribute to supply thereto these necessary 

 aliments in the form of ammonia and carbon compounds. 



The arborescent forms of the forest flora of the British 

 Islands are not very numerous, but (native and denizen 

 species included) they are sufficiently varied as respects 

 chemical interest and instructiveness. For instance, in the 

 first place, let us study the chemical characteristics of the 

 Gymnosperms, taking as an example that stately and sombre- 

 foliaged occupant of sandy wastes and craggy mounds known 

 as the Scots Pine (Pinus sylvestris). Perhaps heretofore 

 we have regarded the leaf as the most vigorously active of the 

 vegetable organs, but here we see that much of the total 

 energy is assigned to the woody tissues. For it is there that 

 the resin, so characteristic of the Coniferae, prevails. Some 

 specially active parent-cells of the heart-wood contain an 

 opaque plasma which divides again and again, and thus forms 

 a group of several daughter-cells, which separate internally 

 (schizogenous), and so leave a hollow space (resin-passage), 

 wherein there flows the product of their spent and exhausted 

 activity (deassimilation), viz., volatile oil and resin. Then, 

 again, the starch and fatty constituents of the wood undergo 

 curious transformations, or rather alternations. During the 

 winter there is no starch whatever in the wood, pith, or bark, 

 the wood at this time bearing much fat-oil which vanishes in 

 April, leaving only a faint residue thereof during the entire 

 summer. Likewise the leaves (really twigs) are free from 

 starch in winter, but about April 1st, whatever the weather 

 may be, and although the chlorophyll therein is oily and 

 inactive, these organs are found crammed with starch, i.e., in 

 circumstances and conditions that in most dicotyledons would 

 assuredly preclude this effect ; and the quantity of this starch 

 gradually diminishes, and disappears altogether in mid- 

 October. Coniferous leaves in their most developed condition 

 are always poorer in nitrogenous, carbohydrate, and mineral 

 (ash) constituents than those of deciduous trees, and the ash 

 is also of a somewhat different composition. Hence we learn 

 that our arborescent Gymnosperms (pines and firs) are subject 

 to a fitful periodicity of life-energy interrupted by pretty long 

 periods of repose akin to hibernation, all preordained and 

 operative in the first place in the formed leaves, ere the buds 

 are evolved or the cambium has awakened. A speciality, too, 

 is the strong accumulation of " dry substance " in the 



tissues under the form of resins, waxes, volatile oils, tannins, 

 tannoids, glucosides, phlobaphenes, and lignin (but not acids), 

 while, on the other hand, the relative amount of starch, fat- 

 oil, carotin, chlorophyll, and albuminoids is comparatively 

 small. 



Reviewing now the more familiar field of the Dicotyledons, 

 and in the first place the various species of Elm (Ulmus 

 campestris, and so on), we are arrested at once by the 

 presence of a very troublesome constituent known as 

 vegetable mucilage. In the cortex, special sacs or canals 

 evolved from the meristem, and in the leaves cellulose- 

 encased roundish compartments in the epidermises, petioles, 

 and nerves contain mucilage in large quantity. It is a 

 degradation product of cellulose provoked by the great undue 

 pressure of growth : it swells enormously in water, and has an 

 acidic function. Some resin occurs in elm bark and wood 

 parenchyma, but the quantity of tannin is decidedly scanty in 

 all parts of the tree. The leaves contain much carotin, wax, 

 albuminoids, and sugars at all times, and their starch- 

 producing power is extremely vigorous. In fact, the tree 

 is a very distinctive starch-tree, and it retains most of it in 

 winter, little or no oil appearing then in the tissues. The 

 average amount of transpiration is only moderate, its flowers, 

 fruits, and leaves grow rapidly, but are short-lived, as the lavish 

 fortification of its bark, leaves, and even fruits, with lime and 

 silica, attests, and some of its varieties are even capable of 

 forming a primary persistent periderm, albeit only feebly 

 suberified. 



Passing on now to those nearly allied, closely related 

 (taxonomically) congeners, the Birch and the Alder, we begin 

 to realise the supreme value of chemical analysis as applied in 

 the world of plants. Both are fat-trees, for in winter the 

 starch vanishes from the pith, wood, and bark, because the 

 leaves produce little starch, and the general reserve thereof 

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

 Birch the process of deassimilation is not so complete as that 

 in the Alder. In the Birch it is not pushed much beyond the 

 production of waxes, resins, and volatile oils, and hence the 

 tannins, phlobaphenes, pigments, and so on, are comparatively 

 sparse. Hence in the " queen of the woods " we observe 

 a silvery-whitish bark, of ghastly aspect by moonlight, con- 

 taining some twelve per cent, of a white hydrocarbon (betulin), 

 easily resinifying in the air, but only about five per cent, or 

 less of tannin, and very little hidden phlobaphene. The 

 phellogen that works this effect is stimulated to action by the 

 rapid growth of the very sappy internal tissues. On the other 

 hand, in Alder bark there is found sometimes as much as 

 twenty per cent, of a powerfully astringent tannin, together 

 with some emodin, which is a higher product of deassimilation 

 again. This tannin penetrates freely into the medullary rays, 

 parenchyma, and pith of the wood (birch-wood is almost free 

 from tannin) ; and although it does not conduce much to 

 lignification, it renders the wood very resistant to the action of 

 water. Birch leaves produce more starch, cellulose, fibre, 

 wax, volatile oil, resin, ash, silica, and soluble salts than Alder 

 leaves do ; but these, on the contrary, contain much more 

 nitrogenous matters, and more fat-oil, tannin, pigments, acids, 

 lime, and manganese. Thus we come to perceive that more 

 fundamental differences exist between these two tenants of the 

 forest than what a mere recital of the few and slight specific 

 characters (chaff-like or woody, falling or remaining scales of 

 the seed-bearing catkin, and so on) would in any way fore- 

 shadow or prognosticate. 



Certain members of the order Cupuliferae must now claim 

 our attention. As regards the grand old Oak, it may be 

 asserted that no member of the vegetable kingdom has been 

 more exhaustively investigated. All that we need state here, 

 however, is that the amount of starch which it creates and 



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