The leaves, which are borne in pairs at the tumid nodes, are oval in form and have a Dicotyledonous type of venation.
The young tissue of the stelar cylinder, in the case of the modified siphonostele characteristic of the dicotyledonous stem, differs from the adjoining pith and cortex in its narrow elongated cells, a difference produced by the stopping of transverse and the increased frequency of longitudinal divisions.
Coalbearing clays containing fresh-water molluscs and dicotyledonous plants, as also conglomerates, alternate with the sandstones in these Tertiary deposits.
In the plant world, the dicotyledonous angiosperms gradually assumed the leading role which they occupy to-day.
It is of interest to note that the leaves of Gnetum, while typically Dicotyledonous in appearance, possess a Gymnospermous character in the continuous and plate-like medullary rays of their vascular bundles.
Stems. But in nearly all perennial Dicotyledons, in all dicotyledonous and gymnospermous trees and shrubs and in fossil Pteridophytes belonging to all the great groups, certain layers of cells remain meristematic among the permanent tissues, or after passing through a resting stage reacquire menstematic properties, and give rise to secondary tissues.
The dense forests of West Africa contain, in addition to a great variety of dicotyledonous trees, two palms, the Elaeis guincensis (oil-palm) and Raphia vinifera (bamboo-palm), not found, generally speaking, in the savanna regions.
I I, Bennettites seed in longitudinal section, showing the dicotyledonous embryo; p, cotyledons; r, radicle; s, testa.
The work was continued after his death, by his son Alphonse de Candolle, with the aid of other eminent botanists, and embraces descriptions of the genera and species of the orders of Dicotyledonous plants.
The next strata, the Aquila Creek series, contain a well-marked dicotyledonous flora, in which both the form and nervation of the leaves begin to approximate to those of recent times.