Exo
implies "out of" & Endo
implies "into".
Scopic (Watchtower) may refers
to the Archegonium.
The Shoot Apical Meristem of
an Exoscopic Embryo grows "out of" the Archegonium/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
Archegonium/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 & Anthophyta.
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 of the two.
The Hypobasal Cell is consequently, the more internal of the two.
One of these cells will eventually lead to the formation of 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 (Liverworts), Bryophyta (Moss), Sphenophyta (Horsetails) & Lycophyta (Club Moss) 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.
