Gnetum africanum , with Notes on Gnetum scandens. 1131 
with the fibrous layer of the outer integument (middle covering). Thus, at the 
base of the ovule the fibrous layer forms a sort of cup just as it does in 
Bennettites . 
5. The outer integument (middle covering) is complex in structure: in 
G. africanum it remains independent,but in G. scandens it becomes fused with 
the outermost covering. In G. africanum it is composed of an outer zone 
which is made up of alternating strands of parenchyma, each containing a 
vascular bundle, and indurated tissue ; and an inner zone which becomes the 
stony layer of the seed. The inner zone contains a palisade layer and a 
fibrous layer. The fibrous layer is angled in the upper part of the seed, there 
being an angle opposite each vascular bundle. These angles, along with the 
number of vascular bundles, are gradually reduced in number, till at the tip 
of the integument there are only four or five. Here the integument clasps the 
micropylar tube, and the five-angled fibrous zone forms a sort of star, of 
which all the cells are lignified at a very early stage. A similar arrange¬ 
ment of the fibrous layer and a similar palisade layer is found in Bennet¬ 
tites Morierei . 
6. A well-developed pollen chamber is present in the young ovule; as 
it decays the apex of the nucellus hardens and forms a pointed cap of 
lignified tissue. 
7. In the young ovule the three coverings arise close together at the 
base of the nucellus, and the free apical portion of the nucellus is by far 
the largest part of the ovule. As the seed grows the region between 
the two integuments becomes much stretched and forms the greater portion 
of the mature ovule, so that the innermost covering becomes free about 
two-thirds of the way up the nucellus. The free portion of the nucellus in 
the mature seed is very small in proportion to the part developed by inter¬ 
calary growth. The embryo-sac develops between the levels of freedom 
of the two inner coverings ; it is as it expands that the intervening region 
stretches. In the mature seed it projects into the free portion of the nucellus. 
8. The open micropylar tube of the youngest ovules (G. scandens) 
is circular in section, and its lining is strongly cuticularized. After fer¬ 
tilization the tube is closed for some distance by means of a tissue formed 
by division of the epidermal cells, and a ‘ flange ’ is also produced which 
fits tightly over the outer integument. In the older ovule and seeds the 
micropylar canal, where it is still open, is slit-like. The tissues of the 
tube become gradually lignified ; the closing tissue becomes lignified first 
and forms a solid thick-walled central rod. The micropylar tube is re¬ 
markably similar to that of Bennettites Morierei , and this central rod is 
compared with the £ nucellar beak ’ in that seed. 
9. The radial structure of the seed, the short free apical portion of 
the nucellus, the presence of a pollen chamber, the extension of the bundle 
system into the free portion of the inner integument, the complex structure 
