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Show 398 DARWINISM CHAP. - uo-h there arc still indications of vast g~p~ in plants ; a.nd altho o d bt to the very exceptional cond1t10ns our knowledge, due, no ot~ ' f plant remains we now po sess required for the preserva ti_on o s development of the variom; . f more con muou vV d ev1dence o a . According to Mr. Lester F. ar , types of vegetat~n~WOO species of fossil plants have been between 8000. an_ ed . and owing to the careful study described or ~ndiCa; 1 ' ' a laro-e number of these arc of the ne~vati?n ° e:~~~rs or g~nera, and therefore gi vc referable to t_hmr \~~1ch though very imperfect, is prohably ns some .no~wn---:n outlines-of the progressive development accurate I~ Its maih th 1 The following is a summary of of vegetatiOn on t e ear w' d . h f t aiven by Mr. ar .- t e ac s as o . f eaetable life-the cellular phnts- The lowest fo~·m~ o erv silurian deposits in the form of three have been foun~ m t: . and in the whole Silurian formation species of marme a g ' ni'sed We cannot for a moment fif · s have been recog · f ty specie that this indicates the first appearance o suppose, ho~ever, tl e earth for in these same Lower ~~ge~abl~ l~f\h~p~~re ~liahly o;ganised vascular cryptog<~ms Silunan. n)e Ct hse f orm of r ht:l Z ocarps-plants allied to Marsllca G d apxe: Ill -and a very little higher, ferns, lycopods, an cY~n an . zo a, \Ve have indications, however, of a s~ Ill comfers a·pe pneta vr.e aetatw. n m. the carbonaceous shales .a nd t1.n ck more ancl . o f , d~wn in the Middle Laurentian, smce becls o~ gmph~~~eraiknown agency than the vegetable cell bthye rme eaInS s noo f w hich carbon can be extracted from the atmo. F'fth Annual Report of U.S. Geological Survey, 1 Sketeh of Palreobota?y ~~- 1 Sir J William Dawson, speaking of 1883-84, pp. 363-452_, with ~~~tn~~ion of fo~sil Ilants, says : "In my own the v~lue of leaves for t~~u~~t~eterminations of the leave~ of trees co~lfirm~d expenence I have often_ fr 't f the structure of thetr stems. 'Ihns, Ill by the discovery of thetr u~ s o~ ~1 e Dunvegan ·eries we have heech-nn~s the rich cretaceous plant-be shol 1 "' I'ed to Fag' us In the L:\l'anue . tl . me bed wit eaves re.er · · t associated m le sa t. f the Trctpa or water-chestnu , aJH1 beds I determined many yearsd a?o ;l~ss i~ the United States leaves which lie subsequently Lesquereux fou~l t m I ~o~md in collections made on the Red Deer referred to the same gen~s. a er, enx's leaves on the same slab. TJJe River of Canada my fnnts and Jesquer d J~tglans in the same formation was presence of trees of the genera ar'l!ct an have since been obtained of . ilicifierl inferred from their leaves,_ and sp~ClmeJ~s the modern butternut. Still we arc wood with the microscopiC ~tnti? uref ~ n leaves alone are liable to doubt."- willing to admit that deternnna Jons IOJ ' The Geological Iliston; of Plants, P· 196· xrn THE GEOLOGICAL EVIDENCES OF EVOLUTION 399 sphere and fixed in the solid state. These grca,t bed. of graphite, therefore, imply the existence of abundance of vegetable life at the very commencement of the era of which we have any geologicalrecord. 1 Ferns, as already stated, begin in the Middle Rilurian formation with the Eopteris Morrieri. In the Devonian, we have 79 species, in the Carboniferous 6 27, and in the Permian 1 6 species; after which fossil ferns dimini h greatly, though they arc found in every formation; and the fact that fully 3000 living species are known, while tho richest portion of the Tertiary in fossil plants-the Miocene-has only produced 87 species, will serve to indicate the extreme imperfection of the geological record. · The Equisetacero (hor. etails) which also first appear in the Silurian and reach their maximum development in tho Coal formation, are, in all succeeding formations, far less numerous than ferns, and only thirty living species arc known. Lycopodiacere, though still more abundant in the Coal formation, are very rarely found in any succeeding depo ·it, though the living species are tolerably numerous, about 500 having been described. As we cannot suppose them to have really diminished and then increased again in this extraordimtry manner, we have another indication of the exceptional nature of plant preservatio.n and the extreme and erratic character of the imperfection of the record. Passing now to the next higher division of pla.nts-the gymnosperms-we find Coniferro appearing in the Upper Silurian, becoming tolerably abundant in the Devonian, and reaching a maximum in the Carboniferou , from which formation more than 300 species are known, equal to the number recorded as now living. They occur in all succeeding formations, being abundant in the Oolite, and excessively so in the Miocene, from which 250 species have been described. The allied family of gymnosperms, the Cycadacere, first appear in the Carboniferous era, but very scantily; are most abundant in the Oolite, from which formation 116 species are known, and then steadily diminish to the Tertiary, although there are seventy-five living species. We now come to the true flowering plants, and we first 1 Sir J. William Dawson's Geological History of Plants, p. 18. |
