COMPLEX HISTORY OF COAL. 361 



2dly, that among these Cryptogamic plants, the Equisetaceae 

 attained a gigantic size ; 3dly, that Dicotyledonous plants, 

 which compose nearly two-thirds of living Vegetables, 

 formed but a small proportion of the Flora of these early 

 periods.* 4thly, that although many extinct genera, and 

 certain families have no living representatives, and even 



* The value to be attached to numerical proportions of fossil Plants, ia 

 estimating the entire condition of the Flora of these early periods, has been 

 diminished by the result, of a recent interesting experiment made by Prof. 

 Lindley, on the durability of Plants immersed in water. (See Fossil Flora 

 No. xvii. vol. iii. p. 4.) Having immersed in a tank of fresh-water, during 

 more than two years, 177 species of plants, including representatives of all 

 those which are either constantly present in the coal measures or universally 

 absent, he found : 



1. That the leaves and bark of most dicotyledonous Plants are wholly 

 decomposed in two years, and that of those which do resist it, the greater 

 part are Conifera and CycadecR, 



2. That Monocotyledons arc more capable of resisting the action of wate.'', 

 particularly Palms and Scitamincous Plants ; but that Grasses and Sedges 

 perish. 



3. That Fungi, Mosses, and all the lowest forms of Vegetation disappear. 



4. That Ferns have a great Power of resisting water if gathered in a 

 green slate, not one of those submitted to the experiment having disappeared, 

 but that ihcxT fructification perished. 



Although the results of this experiment in some degree invalidate the 

 certainty of our knowledge of the entire Flora of each of the consecutive 

 Periods of Geological History, it does not affect our information as to the 

 number of the enduring Plants which have contributed to make up the Coal 

 formation ; nor as to the varying proportions, and changes in the species of 

 Ferns and other plants, in the successive systems of vegetation that have 

 clothed our globe. 



It may be farther noticed, that as both trunks and leaves of Angicspermous 

 dicotyledonous Plants have been preserved abundantly in the Tertiary for- 

 mations, there appears to be no reason why, if Plants of tUs Tribe had 

 existed during the Secondary and Transition Periods, they piould not also 

 occasionally have escaped destruction in the sedimentary (bposites of these 

 earlier epochs. 



In Loudon's Mag. Nat. Hist. Jan, 1834, p. 34, is «« account of some 

 interesting experiments by Mr. Lukis, on successivr changes in the form 

 of the cortical and internal parts of the stems o*" succulent plants, (e. g. 

 Sempervivum arboreum) during various stages ot decay, which may illus- 

 trate analogous appearances in many fossil plarxis of the coal formation. 



VOL. I. — 31 



