326 Saxton. — Contributions to the Life-history of 
feature. In Callitris and Actinostrobus we have clearly an advance from 
the condition found in Widdringtonia , in the fact that sterilization occurs 
before any differentiation of sporogenous tissue is visible. This is, of course, 
only theoretical, as there is no means of distinguishing sporogenous tissue 
until it becomes microscopically visible. 
At a slightly later stage than that described above, the mother-cell 
nucleus is found in synapsis (Fig. 5). At this time the cell has elongated 
somewhat and its wall has thickened considerably. 
Further stages to illustrate the reduction divisions have unfortunately 
been missed, but Fig. 6, which shows a uninucleate megaspore, indicates 
that probably three cells, or at least three nuclei, are formed by the 
divisions of the mother-cell ; but this cannot be stated with any certainty. 
In any case, the other megaspores very rapidly disorganize, and after one 
or two divisions in the functional megaspore can no longer be distinguished. 
The presence of a number of starch grains in the uninucleate megaspore is 
noteworthy, as they are not found either just before or just after this 
stage. 
3. The Female Gametophyte. 
Fig. 7, of a binucleate megaspore, shows that vacuolation only occurs 
between this and the eight-nucleate stage. The latter is shown in Fig. 8, 
which is a drawing of a whole ovule, serving also to illustrate the general 
structure of an ovule at this time as compared with the stage shown in 
Fig. 3. 1 The micropyle is now closed, the micropyle-closing cells appearing 
septate in the figure, due to their growing in a slightly different plane to 
that of the section. They are actually, however, usually, if not always, 
non-septate, as may be seen in transverse sections of the micropyle at the 
same stage. The transverse section closely resembles that of the micropyle 
of Widdringtonia , and has not been figured. 
The upper part of the nucellus consists at this time of cells with thick 
walls and dense contents. These cells never divide and appear to be dead 
or dying, and the pollen-tubes do not now extend below this tissue, which 
is sharply differentiated from the meristematic tissue below it. The young 
embryo-sac lies a good deal nearer the base of the nucellus than is the case 
in Callitris , but is not so deeply placed as in Widdringtonia. The cells 
below the embryo-sac are in somewhat regular longitudinal rows, with 
dense contents, but are not quite so distinctly differentiated in this respect 
as are those of Callitris. 
The early divisions of the nuclei, which lie in the lining layer of 
protoplasm in the embryo-sac, are simultaneous, but whether this applies to 
the later divisions has not been determined. 
Cell formation is similar to that in Widdringtonia , alveoli being 
1 Fig. 3 and Fig. 8 are not, however, drawn to the same scale. 
