If we take a general review of the remains of terrestrial Vegetables, that are distributed through the three great periods of geological history, we find a similar division of them into groups, each respectively indicating the same successive diminutions of Temperature upon the Land, which have been inferred from the remains of the vegetation of the Sea. Thus, in strata of the Transition series, we have an association of a few existing families of Endogenous Plants,[1] chiefly Ferns and Equisetaceæ, with extinct families both Endogenous and Exogenous, which some modern botanists have considered to indicate a Climate hotter than that of the Tropics of the present day.
In the Secondary formations, the species of these most early families become much less numerous, and many of their genera, and even of the families themselves entirely cease; and a large increase takes place in two families, that comprehend many existing forms of vegetables, and are rare in the Coal formation, viz. Cycadeæ and Coniferæ. The united characters of the groups associated in this series, indicate a Climate, whose temperature was nearly similar to that which prevails within the present Tropics.
In the Tertiary deposites, the greater number of the
families of the first series, and many of those of the second,
disappear; and a more complicated dicotyledonous[2] Vegetation
occurs in Lias at Lyme Regis, and at Boll in Wurtemberg; and F. Targionii in the Upper Greensand near Bignor in Sussex.
- ↑ Endogenous Plants are those, the growth of whose stems takes place by addition from within. Exogenous are those in which the growth takes place by addition from without.
- ↑ Monocotyledonous Plants are those, the embryo of whose seed is made up of one cotyledon or lobe, like the seed of a Lily or an Onion. Dicotyledonous Plants are those, the embryo of whose seed is made up of two lobes, as in the Bean and Coffee-seed. The stems of Monocotyledonous Plants are all Endogenous, i. e. increase from within by the addition of bundles of vessels set in cellular substance, and enlarge their bulk by addition from the centre outwards, e. g. Palms, Canes, and Liliaceous plants. The stems of Dicotyledonous Plants are all Exogenous,
