Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/365

 Rh 2dly, that among these Cryptogamic plants, the Equisetaceæ 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. The value to be attached to numerical proportions of fossil Plants, in 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 2 years; and that of those which do resist it, the greater part are Coniferæ and Cycadeæ.

2. That Monocotyledons are more capable of resisting the action of water, particularly Palms and Scitamineous Plants; but that Grasses and Sedges perish.

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

4. That Ferns have a great Power of resisting water if gathered in a green state, not one of those submitted to the experiment having disappeared, but that their fructificatian 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 further noticed, that as both trunks and leaves of Angiospermous dicolyledonous Plants have been preserved abundantly in the Tertiary fprmations, there appears to be no reason why, if Plants of this Tribe had existed during the Secondary and Transition Periods, they should not also occasionally have escaped destruction in the sedimentary deposites of these earlier epochs.

In London's Mag. Nat. Hist. Jan. 1834, p. 34, is an account of some interesting experiments by Mr. Lukis, on successive changes in the form of the cortical and internal parts of the stems of succulent plants, (e. g. Sempervivum arborenm) during various stages of decay, which may illustrate analogous appearances in many fossil plants of the coal formation. 4thly, that although many extinct genera, and