Campbell .— The Embryo-sac of Pandanus. 777 
little change for some time, but they finally disintegrate and are visible 
only as two small, darkly stained, shrunken bodies lying above the apex of 
the embryo-sac. In these early stages Pandanus closely resembles the 
ordinary Angiosperms, except for the vertical division in the upper sporo- 
genous cell. It differs from Peperomia and Gunner a, which in some 
respects resemble it more nearly than any other Angiosperms, in the forma¬ 
tion of three cells which may be interpreted as megaspores, instead of 
having the primary sporogenous cell develop directly into the embryo-sac. 
At what stage the reduction divisions in the nuclei occur could not be 
determined, since for some reason, perhaps owing to the time of day at 
which the material was collected, no nuclear divisions could be found. 
The young embryo-sac (e. s.) is easily recognizable, the cytoplasm 
being noticeably more densely granular than the adjoining cells of the 
nucellus, and the nucleus is somewhat larger. The position of the nucleolus 
lying in the cytoplasm next to the nucleus, as shown in the figure, is no 
doubt the result of an accident. 
Fig. 4, PI. LIX, shows a slightly more advanced stage. In this case the 
upper sporogenous cell is smaller and the nucleus less conspicuous than 
usual. The cytoplasm of the young embryo-sac contains many vacuoles 
and the conspicuous nucleus occupies the centre of the cell. A slightly 
older stage is shown in Fig. 5. The sister cell of the young embryo-sac 
divides longitudinally, instead of transversely, as is the case in most 
Angiosperms. This has, however, been noted in a number of other forms, 
both Monocotyledons and Dicotyledons. 1 
The young embryo-sac increases rapidly in size and the nucleus 
divides, one of the daughter nuclei moving to the upper end of the sac, the 
other to the chalazal end. The two nuclei are quite similar in appearance 
(Fig. 7), and the cytoplasm still fills the whole cavity of the sac, 
although there are several large vacuoles. These vacuoles finally unite, 
and by the time the second mitosis is complete, a single large vacuole 
occupies the greater part of the sac, the cytoplasm being mainly confined 
to the ends, while there is only a thin layer lining the lateral walls (Figs. 8 
and 9). 
Up to this point Pandanus agrees exactly with the typical Angio¬ 
sperms, but the later history of the embryo-sac is decidedly different. 
The two nuclei at the micropylar end of the sac remain for a long time 
undivided, and the next nuclear divisions are confined to the chalazal 
region. Stages with four, six, eight, and twelve nuclei at the chalazal end 
were met with, but in all of these there were but two micropylar nuclei. 
The cytoplasm in the basal region of the embryo-sac increases very much 
in amount as the nuclear divisions proceed. None of the nuclei at this 
stage were found in division, so that the sequence of nuclear divisions in 
1 Coulter, J. M., and Chamberlain, C. J. : Morphology of Angiosperms, 1903, pp. 75, 76. 
