1910] SAXTON—WIDDRINGTONIA 35 
the apical part becoming very narrow and closely resembling the tip 
of an advancing pollen tube. The breaking down of certain cells 
in the axis of the nucellus, facilitating the upward growth of the pro- 
thallus, has already been referred to. The divisions of the nuclei 
are doubtless simultaneous until at least 64 are present (exactly that 
number having been counted in serial sections), and possibly until 
wall formation begins. Fig. 17 shows in outline the general structure 
of the nucellus at the time when 64 nuclei line the embryo sac. Fig. 
18 is part of a tangential section of the prothallus after free nuclear 
divisions have ceased. The nuclei each contain a single nucleolus 
which can invariably be seen to be hollow. 
Cell formation takes places as in most other gymnosperms, and 
has already been described and figured (10, fig.g). A large number 
of nuclear divisions have been seen in the “alveoli,” certain features 
of which strongly recall the peculiar divisions described by LAwson 
(4) as occurring at this time in Cryptomeria. All the earlier phases 
(figs. 19 and 20) are quickly passed through, but that shown in fig. 21 
is very persistent, the marginal fibers having almost the appearance 
of a cell wall. The wall between the nuclei, however, is always 
developed, but in cases where its width does not nearly equal the diam- 
eter of the cell, it is just possible that wall and fibers may disappear 
again and thus give rise to a binucleate cell. It has not been demon- 
strated, however, that binucleate cells ever originate in this way, and 
the chief interest of fig. 23 is in providing a connecting link between 
the very peculiar divisions giving rise to the temporarily binucleate 
cells of Cryptomeria and the ordinary mitotic divisions in normal 
conifer prothalli. 
Very soon after cell divisions are complete, the archegonium 
initials make their appearance. ‘These become considerably larger 
than the surrounding cells and their nuclei are a little larger (fig. 22). 
The position of the archegonia’is somewhat variable, but usually 
two distinct types seem to be formed: (1) a single group of about 
ten or more, directly abutting on the swollen end of the pollen tube;° 
(2) one, or usually more than one, group of few or several archegonia 
(rarely a single archegonium) which are found near, but not abutting 
on, the upper part of the pollen tube, and deep-seated in the prothal- 
6 In the few cases where two pollen tubes reach maturity, a group of this kind 
is organized in connection with each tube. 
