468 Oliver . — The Ovules of the older Gymnosperms . 
are seen the free arillus (a.) and integument (i.) covering the 
free portion of the nucellus. The wall of the nucellus is thin, 
and the contained embryo-sac and endosperm are continued 
towards the base of the seed, as also are the arillus and integu- 
ment. Two bundles enter the seed at the base, and whilst each 
may divide into two or more branches 1 in passing upwards, 
these branches unite again below the level at which arillus 
and integument are free from one another in the principal 
plane of the seed (/.). At this point the central portion 
of the reunited bundle dips suddenly inwards, penetrating the 
stony layer at a special shield-like area. 
The two shield-like areas, right and left of and a little 
below the micropyle, form characteristic marks on the stone 
of the ripe seed when stripped of its fleshy arillus. The view 
of the stone in Fig. 13 shows one of these shields with the 
foramen (a dot) perforating it. The crescent-shaped area 
at the top of the seed, often covered by a thin translucent 
membrane, represents the outer surface of the integument 
where it is free from the arillus. It is noticeable that this area 
attains its greatest downward extension in the plane at right 
angles to the principal plane, whilst in the principal plane (p.) 
(i. e. the one which traverses the foramina) it is much narrower. 
Identical relations obtain between nucellus and integument. 
After its passage through the stony layer of the integu- 
ment, and as it traverses the soft tissue which lies between 
the internal aperture of the foramen and the base of the 
groove between nucellus and integument, the tracheal strand 
forks, the branches turning sharply away from the principal 
plane of the seed. These branches direct their course towards 
the groove between the nucellus and integument, striking the 
furrow of the groove a little below its highest point. These 
relations are somewhat elucidated in Fig. 14, a nearly trans- 
verse section across the seed at the level of the foramina. 
Outside is the arillus, then the stone (shaded dark) with 
a lining of soft parenchyma. The bridge which traverses the 
figure vertically is the nucellus joined to the integument above 
1 This branching is very marked in T. nucifera. 
