A developmental study of the integument in Gymnosperms 3. Ephedra Distachya L. and E. equisetina Bge.
Acta botanica neerlandica , Volume 34 - Issue 1 p. 33- 48
The early ontogeny of the two ovular envelopes of Ephedra distachya and E. equisetina was thoroughly studied as a part of the comprehensive investigations on the integument and associated structures in Gymnosperms. The outer envelope is initiated as a horseshoe-shaped primordium at the ventral (or axial) and lateral sides to become continuous later on; this envelope grows out more rapidly at the lateral sides, so that the young envelope appears as two opposite projections; the mature envelope is a stout structure vascularized at the lateral sides. The inner envelope, which is initiated a little later than the outer one, arises as a ring-shaped primordium and elongates, more conspicuously so at the ventral side, and finally forms a long micropylar tube. Although the greater part of the inner envelope is of a uniform thinness, the basal part swells up appreciably. Histologically the outer envelope is formed by derivatives of both the dermal and the subdermal cells of the ovule primordium (i.e., it is of dual origin), but the inner envelope exclusively by derivatives of the dermal cells except in its basal part (i.e., it is of dermal origin). Evidence from the morphology and anatomy does not support the homology between the two envelopes and suggests that the outer envelope resembles vegetative leaves more than the inner one. The possible numbers and arrangements of the constituting elements of the envelopes are also discussed.
|541324.jpg Cover Image , 14kb|