JT« . i .; GRAY AM> H00KE6 ON THE ROOKY MOUNTAIN FLORA. 73 



these Bame types, also the Ailantus, Gingko, and i goodly number of coniferous genera 

 I cannot point to any types tending to makeup the deficiency ; thai is, to any n«>t 

 either in East North America or in Northeast Asia, or in both. ( edrns, the true Cedar, 

 which comes near i<> it, is only North African and Asian. I need not say that Europe 

 has no Sequoia, and slnuvs no special t \ ■;••• w n h ( ialifbrnia. 



Now the capital fart is that many ami perhaps almost all of these genera of trees 

 were well represented in Europe throughout the Later Tertiary times, it hadnot 

 only the same generic types, but in some cases even the same species, 01 what must 

 ■ iss i- such, in the lack of recognizable dist [notions bet ween fossil remains and Living ' 

 analogues. Probably the European Miocene forest was about as rich and rarious as 

 is ours of the present day, and very like it. The Glacial period came and passed, and 

 these types have not survived there, nor returned. Bence the comparative povertj 

 of the existing European sylva, or, at least, the probable explanation of the absem e 

 of those kinds of trees which make the characteristic difference. 



Why did these trees perish out of Europe, but survive In America and Asia I Before 

 we inquire how Europe lost them, it may be well to ask how it got them. How came 

 these American trees to be in Europe I And among the rest, how came Europe to 

 have Sequoias, now represented only by our two Big-trees of California I It actually 



wed two species and more — one so closely answering to the Redwood of the 

 ranges, and another so very like tin- Sequoia gigantea of the Sierra Nevada, that) if 

 such fossil twigs with leaves and cones had been exhumed in California instead of 

 Europe, it would confidently be affirmed that we had resurrected the veritable ances- 

 tors of our two giant trees. Indeed, so it may probably be. " Caelum son tmimwm 

 mutant ," <fcc, may be applicable eveu to such wide wanderings aud such vast inter- 

 vals of time. If the specific essence has not changed, and eveu if it has suffered some 

 change, genealogical connection is to be inferred iu all such cases. 



That is, in these days it is taken for granted that individuals of the same sp< 

 or with a certain likeness throughout, had a single birthplace and are descended from 

 Che Bame stock, no matter how widely separated they may have been either in spa< e 

 or time, or both. The contrary supposition may be made, and was seriously enter- 

 tained by some not very long ago. It is even supposable that plants and animals 

 originated where they now arc. or where their remains were found, But this i> D01 

 science — in other words, it is not conformable to what we now know, and i> an 

 tion that scientific explanation is not to be sough! 



Furthermore, when species of the same genus are not found almost everywhere, 

 they are usually grouped in oue region, as are the Hickories in the Atlantic > 

 tin- Asters and GrOldenrods in North America and prevailingly on the Atlantic side, the 

 heath- in Western Europe and Africa. From this we are led to the inference that all 

 species closely related to each other have had a common birthplace and origin. Bo 

 that, when we find individuals of a species or of a group widely out of the raj 

 their fellows we wonder how they got there. When we find the same species all round 

 the hemisphere, we ask how this dispersion came to p 



Now, a very considerable number of species of her))- and Bhrubs and ■ fev 

 of the temperate /one are found all round the northern hemisphere; many othc 

 found part way round — Borne in Europe and Eastern Asiaf some in Europe and our 

 Atlantic state-, many, as I have said, in the Atlantic state- ami Eastern Asia— fewer 

 (which is curious) common to Pacific States and Eastern Asia, nearer though these 

 countries be. 



We may Bet it down a> useless m for t bis distribution by causes now in 



operation and opportunities now afforded, - . foi distribution across oceans by winds 



and current- and bird-. The-.- ;•. their part in dispersion from].; 



place, by step after step, but Dot from continent to continent, except foz tew things 

 and in a subordinate w i 



tunately we are not obliged to b i aed supp 



what might possiblj have o* i urred :.'••■•• ind then, in the Lapse of time, bj the chance 



