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Show 216 IJARWINIANA. Moreover, th e Torreya of Florida is associat1ed with a yew· an d the trees of this .g rove areh t he on y fy ew- trees o' f E1 as t m.n North Amenca; for t e yew o our Northern woo d s I· s a decumbent shrub. A· yew· -trel e, h is found with Taxodmm m be Perhaps t e same, . temperat e par t s Of Mexico · The only other yews m Ameri.C a grow WI't h the redwoods and the o•t her Tor- reya m. C al '1f orni·a , and e• xtend •n orthw. ard m• to Ore-• yews are also assoCJated With Torreya In Japan' gaonn d. t h ey ex tend westward through Mantchooria and the Himalayas to Western Europe, and even to the Azores Islands, where occurs the common yew of the Old World. · . . S have three groups of coniferous trees whiCh owe . 'b . 'th agree in this peculiar geographical distr~ utwn, Wl ' however, a notable extension of ran~e m t~e case of t h e yew.. 1 · The redwoods' a. nd t.h mr relatives, Tax.-. odium and Glyptostrobus, whwh di~er so as to const~- tute a genus for each of the three regwns; 2. Th~ To.Ireyas more nearly akin, merely a different spemes m eac h ' regw. n ,. 3 · The JBWS ' still more cl.o sely. re. lated while more widely disseminated, of whiCh It IS yet uncertain whether they constitute seven, five, th_ree, or only one species. Opinions differ, and ca~ hardly b~ brought to' any decisiye test. However It ?e deteimined, it may still be said that the extreme drffere~ces among the yews do not surpass those of th~ recogmzed . variations of the European yew, the cultivated races included. . 11 It appears to me that these several !~stances a raise the very same question, only with different de- SEQUOIA AND ITS HISTORY. 217 grees of emphasis, and, if to be explained at all, will have the same kind of explanation. Continuing the comparison between the three regions with which we are concerned, we note that each has its own species of pines, firs, larches, etc., and of a few deciduous-leaved trees, such as oaks and maples; all of which have no peculiar significance for the present purpose, because they ar~ of genera which are common all round the northern hemisphere. Leaving these out of view, the noticeable point is that the vegetation of California is most strikingly 1mlike that of the Atlantic United States. They possess some plants, and some peculiarly American plants, in commonenough to show, as I imagine, that the difficulty was not in the getting from the one district to the other, or in to both from a common source, but in abiding there. The primordially unbroken forest of Atlantic North America, nourished by rainfall distributed th:tougbout the year, is widely separated from the western region of sparse and discontinuous tree-belts of the same latitude on the western side of the continent (where summer rain is wanting, or nearly so), by inimense treeless plains and plateaux of more or less . aridity, traversed by longitudinal mountain-ranges of a similar character. Their nearest approach is at the north, in the latitude of Lake Superior, where, on. a more rainy line, trees of the Atlantic forest and that of Oregon may be said to intermix. The change of species and of the aspect of vegetation in crossing, say on the forty-seventh parallel, is slight in comparison with that on the thirty-seventh or near it. Confining our attention to the lower latitude, and under the |