The venation is radiating.
To a distribution of veins such as this the name of reticulated or netted venation has been applied.
The leaves of Monocotyledons have generally this kind of venation, while reticulated venation most usually occurs amongst Dicotyledons.
A leaf with only a single midrib is said to be unicostate and the venation is described as pinnate or feather-veined.
The leaf in this case is multicostate and the venation palmate.
Some plants, which in most points of their structure are monocotyledonous, yet have reticulated venation; as in Smilax and Dioscorea.
Taking place in a simple leaf with palmate or radiating venation, give origin to lobed, cleft and partite forms.
4) is the general term applied to leaves with radiating venation, in which there are several lobes united by a broad expansioi.
Of parenchyma, like the palm of the hand, as in the sycamore, castoroil plant, &c. The divisions of leaves with radiating venation may extend to near the base of the leaf, and the names bipartite, tripartite, quinquepartite, &c., are given according as the partitions are two, three, five or more.
The term dissected is applied to leaves with radiating venation, having numerous narrow divisions, as in Geranium dissectum.
In Anomochloa there are several nearly equal ribs and in some broad-leaved grasses (Bambuseae, Pharus, Leptaspis) the venation becomes tesselated by transverse connecting veins.
The venation is like that of many ferns, e.g.
The venation is useful as pointing out the number of leaves which constitute a gamosepalous calyx.
(After Duchartre.) the calyx being trifid (three-cleft), quinquefid (five-cleft), &c., according to their number; or they reach to near the base in the form of partitions, the calyx being tripartite, quadripartite, quinquepartite, &c. The union of the parts may be complete, and the calyx may be quite entire or truncate, as in some Correas, the venation being the chief indication of the different parts.
When the union is incomplete, the number of the parts of a compound pistil may be determined by the number of styles and stigmas; when complete, the external venation, the grooves on the surface, and the internal divisions of the ovary indicate the number.
In such carbonaceous impression not only are the form and markings, such as venation, perfectly preserved, but something of the actual structure may remain.
Hence palaeobotanists have found it necessary to adopt a purely :artificial system of classification, based on form and venation of the frond, in the absence of adequate data for a more natural, grouping.
It is, however, probable that a considerable group of true Ferns, allied to Marattiaceae, existed in Palaeozoic times, side by side with simpler forms. In one respect the fronds of many Palaeozoic Ferns and Pteridosperms were peculiar, namely, in the presence on their rachis, and at the base of their pinnae, of anomalous leaflets, often totally different in form and venation from the ordinary pinnules.
This genus, from the Permo-Carboniferous of Autun, is represented by large, fleshy, reniform leaves or leaflets, with radiating dichotomous venation; the vascular bundles have in all respects the structure of those in the leaves of Cycads or Cordaiteae.
The arrangement of the fibro-vascular system in the lamina constitutes the venation or nervation.
(Reticulated venation; primary veins going to the margin, which is serrated.
- Leaf of an Acacia (Acacia heterophylla), showing a flattened leaf-like petiole p, called a phyllode, with straight venation, and a bipinnate lamina.
The venation is strictly parallel, the midrib usually strong, and the other ribs more slender.