The Embryo Sac and Embryo of Gnetum gnemon

Abstract

1. The "antipodal tissue" described by Lotsy as occurring in Gnetum Gnemon at the fertilization stage is a sharply differentiated nutritive tissue developed in the nucellus beneath the embryo sac, which at this stage contains only free nuclei, as described for other species of Gnetum. 2. Embryo formation begins with an excessive, suspensor-like elongation of the fertilized egg, accompanied by free nuclear division and cleavage walls; and the continuation of free nuclear divisions and cleavage walls in the embryonal cell until a multicellular embryo is formed. 3. The endosperm encroaches upon the tissue of the nucellar beak with some irregularity, an irregularity which reaches its extreme expression in Torreya, with its so-called "ruminated" seeds. 4. The inner integument of the ovule is the morphological equivalent of the "inner fleshy layer" of the single integument of other gymnosperms; and the occurrence of two sets of vascular strands is a relatively primitive condition, which has been departed from by Ginkgoales and Coniferales. 5. The chromosome numbers are 12 and 24.