OF THE OVULE OF CHRISTISONIA. 579 
A curious anomaly is here worth recording. In one ovule 
which had passed the fertilization-stage, and in whose embryo-sac 
the two polar nuclei had already fused to form the definitive 
nucleus, two of the sister-cells of the embryo-sac had persisted, 
but were both very much smaller than, and partly distorted by, 
the latter. The cell adjoining the embryo-sac contained four 
nuclei, all closely in contact with each other and containing con- 
spicuous nucleoli. The other cell exhibited but a single nucleus 
to view. Of the many hundreds of ovules examined, this was 
the only one which showed this irregularity (Pl. XX. fig. 15). 
There is variation in different ovules as to the length which 
the incipient embryo-sac may attain before division of the primary 
nucleus takes place. In some it may grow to a considerable 
length, in others remain quite short. 
Shortly before division the nucleus appears greatly swollen and 
curiously vacuolated ; but this may be simply due to the method 
of treatment which the ovules have undergone prior to their being 
sectioned, so that there is probably no importance to be attached 
to these appearances (figs. 9-12). 
At the next stage two nuclei are seen, resulting from the 
division of the first one at each end of the sac (figs. 11, 12). 
Each of these divides again, so that now two nuclei are present 
at either end of the sac. I missed seeing this particular stage, 
the nearest approach to it being an embryo-sac with a single 
nucleus at one end and a nuclear spindle at the other (fig. 13). 
T also failed to obtain any section, exhibiting the next stage to 
this, where each of the two nuclei at either end divide again, so 
that four nuclei are formed at each extremity of the embryo-sac. 
The stage most commonly met with, and of which there was 
most material at hand, was that in which the egg-apparatus 
appeared fully formed and differentiated at the micropylar end. 
Here were usually seen two large elongated synergide, each con- 
taining, either halfway down or towards its upper end, a 
conspicuous nucleus of considerable size, while the lower broader 
end was occupied by a vacuole. The tapering extremities of 
these cells disappeared in the upper end of the embryo-sac 
(figs. 14-18). A third nucleus, equal ‘in size to those of the 
synergide, and likewise surrounded by a membrane of proto- 
plasm, oceurred either at the lower end of these or lying on the 
top of or beneath them in a different plane of the section: this 
is the ovum (figs. 14, 17, 18, ov). Owing to the fact of its often 
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