Embryology of the Dipsacaceæ

Summary

A comparative account of some aspects of the embryology in three members of the Dipsacaceæ,viz., Dipsacus leschenaultii, Scabiosa caucasica andCephalaria ambrosioides is presented. In all the three species the flowers are borne on globose capitula. InCephalaria the outermost flowers in the capitula are functionally male, since the ovule does not develop beyond the initial stages.

The wall of the anther is made up of the epidermis, endothecium, middle layer and tapetum. The cells of the tapetum soon become multinucleate and at a later stage form a periplasmodium. The mature pollen grain is tricolpate with a tube nucleus and two male cells.

In the pendulous tenuinucellate ovule the vascular strand traverses the single massive integument right up to the micropylar end of the ovule. The hypodermal archesporium directly functions as the megaspore mother cell. Double megaspore mother cells are found inScabiosa andCephalaria, and double dyads are seen in the latter. Megasporogenesis proceeds normally and the development of the embryo sac follows the Polygonum type.

The antipodals are organised as cells and inCephalaria they become binucleate.

Surrounding the narrow chalazal end of the embryo sac there is a prominent radiating tissue.