Heilprin.] J-'^ [Jan. 15, 



existed at a comparatively modern period. Botanists have, indeed, long 

 since pointed out the relation existing between the modern coniferous 

 flora of North America and the equivalent Miocene flora of Europe — a 

 relationsliip which might almost be considered an equivalency — and have 

 even hinted at the possible derivation of the one from the other.* 



The singular distribution of the pines makes it certain that neither their 

 vertical nor their horizontal (or longitudinal) range is determined by con- 

 ditions of temperature alone, or, perhaps, even primarily. Humboldt 

 has plainly stated this fact : " This absence from the southern hemisphere 

 of the true Abietineae, of the Juuiperineae, Cupressinese and all the Taxo- 

 dinese, as likewise of the Torreya, of the Salisburia adiantifolia, and of 

 the Cephalotaxus among the Taxinefe, vividly reminds us of the enig- 

 matical and still obscure conditions which determined the original 

 distribution of vegetable forms. This distribution can by no ineans be 

 satisfactorily explained, either by the similarity or diversity of the soil, by 

 thermal relations, or by meteorological conditions." f Mr. Thomas 

 Meehan has repeatedly insisted that the timber line on mountains is not 

 essentially a fixture determined by climate, but depending more par- 

 ticularly upon special topographic features of the surroundings — the 

 character of the soil, amount of downwash, exposure to storms, etc. The 

 critical comparison of different timber lines, taken in conjunction with ver- 

 tical distribution, shows that this contention is at least largely true. The 

 abrupt termination of the forest on some of our mountain heights, whether 

 high or low — as for example on the Eocky Mountains or on Mt. Katahdin 

 — and the continuance of trees of still noble proportions practically to 

 the very limits of disappearance, point very strongly to this conclusion, 

 a conclusion which is further supported by the reappearance in many 

 places (of the same region) of tlie identical forest in positions considerably 

 more elevated (and presumably much better adapted to a special devel- 

 opment). The irregular height to which the "Waldregion " attains on 

 the Alps and on other mountains of Southcentral Europe is certainly 

 attributable at least as much to topographic (physiographic) as to climatic 

 conditions. Thus, on the main body of the Central Alps (460-470 N. 

 lat.), the limit of trees is found at approximately 6400 feet ; in the 

 Southern Alps of Dauphiue (45° N. lat.), at 8300 feet (in places 

 only 5550 feet); on the lUyrian Alps, of Karst, Austria (46° N. lat.), at 

 5000 feet, and on the Dinarie Alps of Bosnia (440 N. lat.), at 5300 feet. 

 So, again, on the Jura mountains, in lat. 47°, this limit is reached at 4900 

 feet, whereas on the Altai, in lat. 50°, it rises nearly 1500 feet higher, 

 or to 6400 feet, t 



The limitation to height of herbaceous plants parallels the history 

 presented by trees. It is generally assumed in their case that the line of 



* Hildebraud, " Die Verbreitung der Coniferen," "Verhaudl. d. natur. Vercines der 

 preuss. Rheinlande uud Westphalens," xviii, p. 377, 1861. 

 t " Physiognomy of Plants," in "Views of Nature," p. 321, Bohn edition, 1850. 

 t Grisebach, " Vegetation der Erde," i, pp. 180 et scq., 1884. 



