Gnetum africanum, with Notes on Gnetum scandens . 1119 
The nucellus is here composed of a very small basal region, from 
which arise the three coverings and a comparatively very large free apical 
portion. 
The inner series of bundles is hardly yet developed. It is interesting 
to find that, at this very young stage, the open micropylar tube is circular 
in transverse section and is lined by cells whose outer walls are already 
thickly cuticularized 1 (Text-fig. 12). 
B. The next stage was seen in the youngest ovules among my material 
of G. africanum. Their micropyles are already either closed or nearly 
so. The three integuments still arise near together at the base of the 
ovule. The vascular system, except in the outermost covering, still 
consists only of strands of cambial tissue, which extend to the tip of the 
outer integument, and run for some distance into the inner integument. 
The integumentary nature of the inner series of 
vascular bundles is clearly seen in the photograph 
shown in Fig. 14, PI. LXXXVII. 
The tip of the micropylar tube is already 
withered, and so firmly interlocked by means of 
the flange with the outer integument, that it is 
often difficult to make sure that there is no actual 
continuity of tissue between them. 
The lining of the micropylar tube has prob¬ 
ably never been so thickly cuticularized as it was 
in the young ovule of G. scandens. In the closed 
region there is often little or no sign of cuticu- 
larization to be seen at this stage, but in the 
withered tip, and often for a short distance 
below the closed region, the epidermis has a thinly cuticularized 
wall. 
A well-developed pollen chamber is present at the apex of the nucellus 2 
(Fig. 14, PI. LXXXVII). At this stage the embryo-sac is considerably 
enlarged, and extends from the level of origin of the middle covering to 
some distance above the origin of the inner integument. 
C. The later stages of development were mostly seen in abortive 
ovules (see Text-figs. 13 A, B, C). The greatest change which takes place 
consists in the gradual stretching and growth of the region between the 
inner and middle coverings. The basal region develops hardly at all in 
length, and the apical or free region of the nucellus also develops com¬ 
paratively very little, but becomes gradually encroached upon by the 
growing endosperm : thus nearly all the growth in length of the seed 
1 The thickness of the cuticle is here more comparable with that in Welwitschia than in other 
species of Gnetum ; Sykes, 1910 (2), p. 196, Fig. 10, PI. XVII. 
2 Lotsy, 1899, p. 94, Fig. 35, PI. V. 
Text-fig. 12. Transverse 
section of micropylar tube of 
young unfertilized ovule of 
G. scandens , showing thick 
cuticularized lining. 
4 D 2 
