As mentioned above, it is believed the suspensor channels nutrients to the embryo until the heart-shape stage. Division of the apical embryonic mother cell produces an axially symmetrical globular embryo, but the protoderm in pea is not formed until the late globular stage, relatively late in comparison with cruciferous plants. In contrast, the formation of the shoot apical dome can be delayed until the time of seed germination in the crucifer, Arabidopsis thaliana . Establishment of bilateral symmetry, by the initiation of two cotyledons to form a heart-shape embryo, is often considered to be a landmark for the end of the proembryo stage. One feature of pea that has not really been noted by previous workers is that it is bilaterally symmetrical symmetry with one plane of symmetry in the embryo.
C otyledon cellular development in relation to storage product accumulation .
The cotyledons of pea are storage organs that accumulate large amounts of starch and protein and a little lipid, for use in seed germination. As mentioned, the cotyledons comprise a storage parenchyma, epidermis and provascular traces. As mentioned earlier, no specialization occurs in the organs with respect to photosynthesis. Nuclear endoreduplication occurs in the cotyledonary parenchyma at the later stages of embryo development. For additional information on embryo development in other plants click here .