Origin and Development of Embryos in Certain Apogamous Forms of Dryopteris

Abstract

Game-tophytes of 4 forms of the D. pseudo-mas complex and D. hirtipes have a similar method of apogamous embryog-eny. No migration or fusion of vegetative nuclei, which might be interpreted as replacing fusion of egg and anthero-zoid, were observed. The embryos arise behind the notch from the lower 2 cell layers (layer 3 and 4) of prothallial cushions 4 cells thick. Layer 3 gives rise to internal tissue, in which tracheids and the apical cell of the first root may arise. Layer 4 gives rise to the apical cell of the stem, its appearance being concurrent with growth in layer 3. The apical cell of the first leaf arises in a segment derived from the apical cell of the stem. Presence of tracheids in the prothallial cushion which bears no embryo is evidence of abortion of an entire embryo through the failure of these apices, with the possible exception of the apical cell of the first root, to differentiate. Tracheids lying in the cushion between the prothallial notch and the insertion of developing embryo are evidences that changes in layer 3 in prepn. for embryo-initiation involved more of the cushion than changes in layer 4. Any organ may abort independently of others.