286 
integument. Within the nucellus is a large embryosak, 
and at the top a characteristic deep pollenchamber is 
formed. After fertilization, when the embryo enlarges, the 
nucellar tissue becomes thin and in the ripe seed it remains 
as a papery membrane. 
The outer integument bears on its inner surface in the 
micropylar region several papillae, serving to close the 
cavity between the micropylar tube and the outer covering. 
In the micropyle itself a drop of mucilage is segregated, 
which becomes a hardened mass after pollination, closing 
the entrance to the pollenchamber. 
At the base a ring of vascular bundles enters the ovule 
and divides into two systems, one running in the outer 
integument, towards its apex, agreeing in number with 
the ribs on the stony coat, and one in the inner inte- 
gument as far below as the level of separation of nucellus 
and integument and consisting of two rudimentary vas- 
cular bundles. 
There are many different views about the value of the 
two coverings of the ovule. Strasburger (147) regards 
the outer coat as equivalent to a pair of leaves but in 
(150) he changes his opinion and calls it outer integument. 
Lignier (58) says that the outer covering is composed 
of a whorl of three leaves, the outer one of which is 
more or less abortive, whilst the inner envelope consists of 
three carpels, of which one only is developed and the 
others rudimental. Van Tieghem too regards the outer 
investment as a fusion of two leaves. Finely there are 
many botanists, who consider them integuments both, but 
in the discussion Ï will return to this. 
