ILLUSTRATIONS (23;. HEIGHTS AT WHICH TREES GROW. 327 



through nourishment derived from the roots, which the 

 extremity of the stem receives from a neighbouring living 

 tree of the same species. The roots of the living tree he 

 conceives are organically incorporated with those of the 

 stump.* Kunth, in his excellent new Lehrbuch der Botanik, 

 is opposed to this explanation of a phenomenon, which was 

 even known, though imperfectly, to Theophrastus.f Accord- 

 ing to him, this process is perfectly analogous to that by 

 which metallic plates, nails, carved letters, nay, even stags' 

 horns become imbedded \vithin the body of wood. "The 

 cambium, that is, the thin, walled cellular tissue, conducting 

 muco-granular sap, from which new formations alone proceed, 

 continues without any relation to the buds (being perfectly 

 independent of them) to deposit new layers of wood on the 

 outermost layer."J 



The relation above alluded to, between the absolute height 

 of the ground and the geographical as well as isothermal 

 latitude, shows itself often, no doubt, when one compares the 

 arborescent vegetation of the tropical part of the Andes chain 

 with the vegetation of the north-west coast of America, or 

 .he banks of the Canadian lakes. The same remark was 

 made by Darwin and Claude Gay in the southern hemisphere, 

 when they, in their descent from the plateau of Chili, ad- 

 vanced towards Eastern Patagonia, and the Archipelago of 

 Tierra del Fuego ; here woods of Drymis Winteri, together 

 with Fagus antarctica and Fagus Forsteri, cover every thing 

 with long uniform rows in a northern and southern direction 

 down to the low lands. Trifling deviations from the law of 

 constant station-ratios between mountain height and geographi- 

 cal latitude, depending or local causes, not sufficiently investi- 

 gated, occur even in Europe. I would call to mind the limits 

 of altitude for the birch and common fir in a part of the Swiss 

 Alps, on the Grimsel. The fir (Pinus sylvestris] flourishes 

 there up to 6330; and the birch (Betula alba] up to 6906 

 feet; beyond them again there is a belt of stone pines (Pinus 

 cembra), whose upper boundary is 7343 feet. The birch, 

 in consequence, lies there between two belts of Coniferee. 



* Gbppert, Beobachtungen uber das sogenannte Umwallen dcf 

 Tannenstocke, 1842, s. 12. 



f Hist. Plant., lib. iii. cap. 7, pp. 59, 60. Schneidei. 



* Th. i. s. 143, 166. 



