SC//i.VC/i-GOSS//'. 



141 



It will lir iiljservfil in \ lew nl llic lorr^joinj^ 

 iicciiunl, thai llic iiu>r|>lii>l<i|jii'al ftMlurcs, anil the 

 lihysical cliaraclcrisliis of ihcse trees are tulcrably 

 Miiiilar. There is, linwcver, one eminent pei u- 

 Ii.irity possibly not sufHciently taken into account 

 ill taxonomy, viz., the very serious difletencu in 

 respect to the leaf. That of llie birth bein;^ 

 pointed, muchnoicheil, glossy, and in form of 

 an isosceles triangle mounted on a slender, rather 

 Innj;, and not downy petiole. The leaf of the 

 alder is roundisli, with a wedge-sha[)ed base, a 

 wavy and only slight!. -toothed margin, hairy and 

 glutinous when young, but later a glossy, dark 

 olive-green on both sides, and is mounted on a much 

 shorter petiole. Uolli leaves clcvelop one or two 

 rows of palisade cells, the lacunar tissue is rather 

 loose, ami the cuticle comparatively thin, with 

 little incrusting matter even in the .autumn ; but 

 the iranspiratory functions are evidently much 

 belter provided for in the case of the aliler leaf 

 than in that of the birch. On the other hanil, 

 juilging from the amount of chlorophyll and 

 carotin, the assimilatory functions are compara- 

 tively inactive. In fact, the chlorophyllian proto- 

 plasm produces in both cases more oil and less 

 starch. According to Kischer, during December, 

 January and Kebruary of each year, the whole of 

 the starch in pith, wooil, ami bark disappears, 

 most of it being Iransformeil into a fatty oil, and 

 a smaller portion in the rind into glucose. The 

 fibre of the ilry alder leaf is about 13.25 per cent., 

 that of the birch is 18.10 per cent., while the 

 amount of mineral matter, ash, is respectively 4.13 

 and 3.52 per cent. The i)roportion of lime, mag- 

 nesia, i>hosphoric and sulphuric acids, is verv con- 

 siderable in both cases, but that of silica is com- 

 paratively small throughout the whole tissues of 

 both trees. In fact, these organisms must be re- 

 garded as fastidiously and i)ronouncedly calcium- 

 needing, with a very small prevailing siliceous con- 

 tent. Both species, again, with the exception of 

 the allieil hornbeam, contain a lower proportionate 

 amount of albuminoids in their foliar organs than 

 in those of any of our ordinary denizens of the 

 forest. The proportion of non-nitrogenous ex- 

 tractive matter, on the other hand, is exceptionally 

 great in the alder leaf; that of the hornbeam coming 

 nearest to it. The amount of similar constituents 

 in the birch leaf is, though still deiidcdh high, at 

 least 6 per cent. less. 



The serious ililTcrenccs, which have now been in- 

 dicated, seem to furnish the key to the whole posi- 

 tion. It is ipiite evident, as aforesaid, that the 

 assimilatory functions of both organs are not emi- 

 nently robust. The more fully and thoroughly 

 the subjects are analysed, the more apparent it 

 becomes that the counterpart thereof, viz., the de- 

 assimilatory process is much more extensive and 

 complete in the case of the ahler llian in that of 

 the birch. If we ex.imine a birch leaf at the period 

 of its highest development, say about the end of 

 July, we find that besides about 50 |)er cent, water, 

 it contains wax, with n little fixed and volatile oil. 



also considerable resin, rutin, and very lill'e 

 tannin, much mucilage, about 2.7 per cent, nitro- 

 genous matters, and 1.7 o-sh. The alder leaf at 

 the corresponding period, contains a darki.sh 

 brown fatty matter, no volatile oil, a little resin, 

 I onsiderable tannin, much mucilage, about 2..> 

 nitrogen, and 2 ash. It will be observed on clos 

 comparison, that while the former organ has ad- 

 vanced to the wax ami resiu-forming stage, the 

 latter has overleaped this stage, and has produceil 

 a considerable quantity of a highly-carbonaceous 

 ami |>liloba[>henic tannin (C27, H28, On), with 

 its attendant colorific consequences. The dark 

 (dive-green of the ahler leaf is due, not to the pre- 

 dominance of chlorophyll and carotin, but partly 

 to the ilarkish fatty matter, still more to the ten- 

 dency which the tannin exhibits of re.idilv forming 

 high red-brown or muildy-shaded anhydrides, that 

 forbid any change of colour in the autumn. The 

 alcoholic extract of the birch leaf, even at the cnrl 

 of .September, contains no phlobaphene, its tannin 

 (C;„, Il.j.j, 0„) is much less carlionaceous, and 

 the brilliant golden yellow of its autumnal livery 

 attests that the products of de-assimilation have not 

 attained the utmost limits of transformaticm. As 

 Grassmann remarked, " Wax is one of the ingre- 

 dients of birch buds, and the sticky balsamic cover- 

 ing of these in the first period of develo])ment is 

 formed very probably of plant wax, chlorophyll, 

 ethereal oil, and some resin." .AH these ingre- 

 ilients, it may be noted, have been formcil in the 

 previous autumn. 



What is true as respects the foliar organs holds 

 good also in the case of the other tissues. Thus, 

 while the bark of the alder sometimes contains as 

 much as 20 per cent, of tannin, that of the birch 

 rarely has over 6 per cent, of the same substance. 

 On the other hand, it contains from 50 to 60 per 

 cent, cuticular substance (suberin), with ^^ per cent, 

 of a white camphoraceous resin, to which it owes 

 its silvery white colour, and only small cjuantilies 

 of bitter principle and mucilage. The same kind 

 of conditions prevail in the wood. In the alder the 

 cells of the medullary rays, the wood-parenchyma 

 and pith, are richly charged with tannin, while in 

 those of the birch it is decidedly ' si)arse, there 

 being none at all in the wood parenchyma. Hence, 

 the wood of its ancient trunk, even when felled 

 and exposed to the air, preserves, if it be stil' 

 sound, a uniform lightish colour. 



The volatile oils and resins of the birch are pro- 

 duct.< that, themselves separate, are cast ofi" outside 

 the tissues. On the oiner hand, the lavish tannins and 

 phlobaphenes of the alder are used in the forma- 

 tion of lignin, incrusting matter, heart-wood, ami 

 timber that stands moisture in an incomp.ar.ibU 

 manner, but on exposure to the air almost in- 

 stantlv assumes a red-brown colour, thus showing 

 the force and tendency which, in another region 

 of its organisation, operates to hold out a sign anc 

 symbol of distinction from the taxonomin-.dlv allieil, 

 but physiologically disparate. Rrliila. 

 Pallcrdah., II 'i:stiiioivlaiid. 



