MORPHOLOGICAL INTERPRETATION OF THE EMBRYOPHYTA EMBRYO WITH APPLICATION TO THE CASE OF GRAMINACEAE (POACEAE)

A new interpretation of the Monocotyledoneae embryo is presented follo wing a reinvestigation of the fundamental transformations characterizi ng the evolution of the zygote to a plantlet, in the Archegoniatae div ision or Embryophyta subkingdom (including Bryophyta). The following e lementary processes of embryogenesis were analysed: segmentation, terr itorial differentiation, histogen differentiation, and organic differe ntiation, the latter being related to the formation of terminal merist ems. Embryos belonging to very different systematic groups are compare d by a diagram showing the development of the essential parts of the e mbryo body. From the different data collected, a diagram is proposed t o represent the embryo of the Gramineae. This includes (i) a foot area (scutellum) homologous to that of Ruppia and those of various Pterido phyta; the foot differentiation also affects a part of the rising coty ledon; (ii) a cotyledon with a coleoptilary sheath; (iii) a lateral pr imary caulinar meristem (shoot apex); (iv) a primary root (radicle), w hich is endogenous because the organic differentiation do not reach th e outside of the body; (v) a coleorhiza, thallin residue of the proemb ryonic stage, separated from the root by a space arising from the dela mination of one of the main proembryo cell walls.