288 
The middle and inner coverings are real integuments 
and are therefore called the outer and inner integument. 
The outer integument arises from the undifferentiated 
mass of tissue at the base of the ovule just above the 
perianth, and is free from the two other coverings, except 
in the above mentioned case of Gnetum scandens, .where 
it is fused with the outermost envelope. At the top it 
expands, forming a thick wall round the lower part of 
the micropylar tube. The outer integument is composed 
of several layers, which are more or less differentiated in 
the several species. The innermost zone contains many 
M sclerotic fibres, which become lig- 
nified and form the sclerotesta. The 
other layers, which are more fleshy, 
but in some species as in Gn. scan- 
dens become lignified too, may be 
distinguished, as Thoday (153) 
does, in an outer fibrous zone, a 
hypodermal strand and a palisade 
layer, but as a whole are comparable 
with a sarcotesta. In its upper part 
the sclerotesta is angular and in 
transverse section is star-like, thus 
giving the impression of being com- 
posed of four or five valves. 
The inner integument is a thin 
Fig. 11. GnetumGnemon:; layer, in the ripe seed represented 
longitudinal section through É shrivelled' sad emo 
the ovule; cupule, outer in- PY 4 papery , 
tegument, inner integument upwards it projects as a long micro- 
with a long micropylar tube 
RE elIOe pylar-tube far beyond the ovulum. 
At its apex the micropyle ends in 
four or five slips, agreeing in number and position with 
the angles on the sclerotesta. 
After fertilization has taken place the micropylar tube 
is closed by a remarkable blocking-tissue at its base, for- 
