Exo
implies "out of" & Endo
implies "into".
Scopic refers to the Gametophyte.
The Shoot Apical Meristem of an Exoscopic
Embryo grows "out of" the Gametophyte
during its initial phase of growth and continues along this trajectory. This is typical for the Hepatophyta, Bryophyta, Psilophyta &
Sphenophyta.
The Shoot Apical Meristem of an Endoscopic
Embryo grows into the Gametophyte initially.
The apex changes its direction of growth, and ultimately grows out of the
Gametophyte. However, this only occurs after a significant amount of Embryonic Shoot
Development has occurred. This is typical for the Lycophyta,
Cycadophyta, Coniferophyta & Magnoliophyta.
You should recall that the Zygote divides transversely to produce and
Epibasal & Hypobasal cell.
The Epibasal Cell is the cell closest to the
Archegonial Neck & is more external.
The Hypobasal Cell is consequently, the more internal of the two.
One of these cells will form the Shoot Apex
which is established early in Embryogeny. The Root Apex arises later.
If the Epibasal Cell forms the Shoot Apex, the Embryo is Exoscopic.
If the Hypobasal Cell forms the Shoot Apex, the Embryo is Endoscopic.
The Embryos of the Hepatophyta, Bryophyta, Sphenophyta & Lycophyta
have absorptive structures called the Foot.
The Foot does not contribute directly to
the axial components (Shoot & Root) of the Embryo. Consequently, it is
not considered to be part of the "Embryo
Proper".
I have drawn the foot as a discernable structure, and it is distinct in the Hepatophyta
and Bryophyta. However, it may be less discrete in other Divisions.
