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Show 400 DARWINISM ( 'JIA 1'. . . tyledons m. tll e Carboniferous and dP' ermian1 meet with monoco f these fossils w:.Ls long 1. pntcc ' formatiO· ns. "''he character 0 1 h l J.. • to be well established ; an< t c S~l ) - but is now behoved t. mall numbers in all succecdl!lg · t be presen 1n s r~ class contmues ? . r lentiful in the U ppcr vrcta ·cons, deposits, becomdm gt r· athth ee Ep e ancl Miocene In the Luter ~ ocen · . a.nd very abun an l.n h been discovered ; but the 11 f> formation 272 species f ~ve larcrer proportion of the total species in the Eocen? orm a o vecrctation of the perwd. 1110 ch h .tcr in the Crctn.crm.ls . 1 1 appear very n • ' . True chcoty ec ons d' · ion if we except a .·mglc l . d l 'n its upper IVI ' " •] )erwd, an on y 1 . b d of Greenland. Ihc 1'CllHn' . f the U ro-o man e s d l 1 specws ro~ o b fi 1 the sub-cla fully eve ope< h. tllat we ere nc l' . . able t mg IS . f t es all the three c lVISlOlls-and in great luxunanc; ;am~pet~l~-being represented, with Apctalro,Polypeta.lro, an 770 species. Among them are .-nch a total of no less than l thp birch the beech, the sy ·antOJ'l', ·1· f as the pop ar, 0 ' f fami mr orms h fi the true laurel, the sassa ras, d h . 1 . as well as t e g, 1' l . an t e oa. c' 1 the walnut the magno m, an< C\ en the persimmon, the map e, 'b Pa ~ing on to the Tertiary l d the phnn tn es. ' . . the . adp p e1 <Ln bcrs m• crease, t'Il l they reach th.m r m:txmmm 1 P . eno t 10. num here more th an ')000 species of < woty- .:.1 • in the Mwcene, w. d Amon<r these the proportiOnate ledons have been .dlscovere . t he h·~s slightly increa cd, but number of the higher gamope a ' . 'd ·ably less than at the present day. 1s consi or Poss~.b le ca~I-Se 0i f S1.l dden late Appeamnce of E;~·ogr' Jis. ranee of fully developed cxogrnons The sudden appea 01 , 1. ·ocl I. s very analouons to 1 t · the Cretaceous p ...., flowenng pan s m f ll the chief types of the equally sudden appearaEnce o a ancl in both cases we l' · the 'ocenc ; placental mamma Ia I~ suddenness is only apparent, dnc. to must feel sure .t~at this. ·h have revented their prcscnatwn unknown conditions ~hie . fp, t' The ca.-e of the ( . i' . ) 1 earher orma Ions. or th 01r c ISCOVCl Y II • pects the 111 os t cxtra-l t is 111 some res dicotyledonous p_an ~ l' Me ozoic formations we appea r ordinary, beca~se m t e ear :c: of. the flora of the period, to have a fan· representatlO f s equisetums cycads, . h · d forms as ern , · ' · includmg sue vane Th only hint at an cxphtnn.- conifers, and monocotyledons. . e b Mr BaH who supposes tion of this anomaly has been giVen y . ' XII[ TIIE GEOLOGICAL EVIDENCES OF EYOLUTION 401 that all these groups inhabited the lowlands, where there was not only excessive heat and moisture, but also a superabundance of carbonic acid in the atmosphere-conditions under which these groups had been developed, but which were prejudicial to the dicotyledons. These latter are supposed to have originated on the high table-lands and mountain ranges, in a rarer and drier atmosphere in which the qua.ntity of carbonic acid gas was much less ; and any deposits formed in lake beds at high altitudes and at .-nch a remote epoch have been de troycd by denudation, and hence we have no record of their existencc. 1 During a few weeks spent rcccn.tly in the Rocky Mountain , I was struck by the great scarcity of monocotyledon and ferns in comparison with dicotyledons-a scarcity due apparently to the dryness and rarity of the atmosphere favouring the higher gronps. If \YO compare Coulter's Rocky Mountain Botany with Gray's Botany of the JVorthenL (East) United States, we have two areas which differ chi efly in the points of altitude and atmospheric moisture.. Unfortun~tcly, in neither of these works arc the spcc10s consecutively numbered; but hy taking the pages occupied by the two divisions of dicotyledons on the one hand, monocotyledons and ferns on the other, we can obtain a good approximation. In this way we :find that in the flora of the North-Ea. tern States the monocotyledons and ferns are to the dicotyledons in the proportion of 45 to 100; in the Rocky Mountains they are in the proportion of only 34 to 100 ; while if we take an exclusively Alpine flora, as given by Mr. Ball, there are not one-fifth as many monocotyledons as dicoty lcclons. These facts show that even at the present day elevated plateaux and mountains are more favourable to dicotyledons than to monocotyledons, and we may, therefore, well suppose that the former originated within such elevated areas, and were for long ages confined to them. It is interesting to note that their richest early remains have been found in the central regions of the North American continent, where they now, proportionally, most abound, and where the concbtions of altitude and a dry atmosphere were probably present at a very early period. 1 "0~ the Origin of the Flora of the European Alps," Proc. of RO'IJ. Geog. Society, vol. i, (1879), pp. 564-588. 2 D |