J S S Mohan
Articles written in Proceedings – Plant Sciences
Volume 91 Issue 3 June 1982 pp 189-200
Leaf architecture including venation pattern has been studied in 19 genera and 29 species of the Apocynaceae. The leaves are simple, alternate, opposite or whorled with entire margin and a simple midrib. The major venation pattern conforms to pinnate camptodromous type with festooned brochidodromous secondaries. The qualitative and quantitative features are charted. The leaf size, areole size, number of vein endings entering the areoles and number of vein terminations entering the areoles vary from species to species even within the same species. The highest degree of vein order is observed up to 7°. Isolated tracheids, isolated vein endings, isolated free vein endings and tracheoidal elements are noticed. Bundle sheath cells ensheaths all category of veins.
Volume 99 Issue 5 October 1989 pp 423-429
In some Apocynaceae a group of 10–15 resin glands is present as finger-like projections on the adaxial side of the proximal end of the petioles and sepals or petals. They originate from a group of epidermal and sub-epidermal cells. At maturity the glands are differentiated into a short stalk and a clavate head. The latter is composed of epidermal secretory cells and sub-epidermal parenchyma. Structurally and ontogenetically the resin glands resemble extrafloral nectaries and the standard colleters of the Rubiaceae. However, histochemical tests for lipophilic substances revealed that these glands secrete resin. The pale yellow, viscous secretion is released by cuticular bursting and covers the tender shoot apices and developing buds. The position and the secretory activity of the resin glands in relation to their function is discussed.