627 
Ovule of Boivenia spectabilis. 
are to supply the ovule can be seen as procambiai strands in the sporophyll. 
The changes which take place in the ovule as growth proceeds can easily be 
followed in the slightly older ovules. All the parts become larger and more 
differentiated, but the most marked change is that which occurs at the apex 
of the ovule in the free parts of nucellus and integument. In the ovule just 
described the nucellus had a broad flat top, almost on a level with the 
slightly rounded top of the integument and only separated from it by a 
slight cleft (Text-fig. 1). From this time onwards the parts of the integu- 
ment and nucellus above the cleft show marked growth. The epidermal 
cells actively divide by periclinal walls and gradually build up the free 
areas of nucellus and integument. As the nucellus grows its sides gradually 
become sloping, while the top remains flat, so that the whole of the free 
part resembles a truncated cone (Text-fig. 2). The integument keeps pace 
in the growth and follows closely the sloping surface of the nucellus, the 
apex of which gradually becomes more pointed (Text-fig. 3). The nucellus 
for some time grows at the same rate as the integument, and the two are 
therefore of about the same height, but at the stage seen in Text-fig. 3 the 
integument has begun to outgrow it. From this time onwards the free 
ends of the integument grow more rapidly than the nucellus, and the 
micropyle between becomes gradually narrower. 
A very similar method of growth of nucellus and integument was 
described in Stangeria , and photographs 2, 7, and 12. PI. XVII 1 compare 
very closely with Text-figs. 1-3 of this paper. 
1 Lang, loc. cit. 
T t 2 
