1903] EMBRYO SAC OF CASUARINA . 10g 
the end is separated from the main body, as Treub claims, or 
not. When it approaches the sac that it ultimately fertilizes, it 
is sometimes free (jig. 20), and sometimes apparently within the 
prolongation of the very sac whose egg apparatus it is destined 
to reach (fig. 27). I doubt whether there is any fixed path 
within the nucellus for the tube. It probably follows the path 
of least resistance so long as it leads in the direction whence 
comes the guiding stimulus, whatever that may be. 
The sperms were observed near the chalaza in several prepa- 
rations, as small rounded nuclei accompanied by the tube nucleus 
(figs. 18, 19). They were again seen, still spherical, in the tube 
near the sac about to be fertilized (fig. 27), and here too the 
tube nucleus was close behind them. This nucleus is easily dis- 
tinguished from the sperms by its comparatively large size. In 
jig. 20 the sac, which is evidently quite near the point of fertiliza- 
tion, shows only two antipodals, and there is one nucleus mis- 
sing in the egg apparatus. The nuclei f are probably the two 
polars. It would be possible to regard these as two endosperm 
nuclei, but no reason for doing so appears. 
Fig. 217 is a case of ‘double fertilization.” In this the tube, 
or its contents, apparently entered by way of the antipodal pro- 
longation. The sperms are crescentic bodies, one slightly larger 
than the other. The two polar nuclei have not yet united. I 
see no reason for any other interpretation of the two polars; if 
they are endosperm nuclei, we have a unique case in the fusion 
of a sperm with endosperm. Which of the three micropylar 
nuclei is the egg I cannot say, but it is probably the one con- 
taining the larger spherical nucleus, or that containing the elon- 
gated nucleus. No antipodals are in evidence, but they are 
probably in the antipodal prolongation. The sperms evidently 
elongate within the sac or very near it, as in Asclepias (2). 
Iam convinced that no such endosperm formation before fer- 
tilization occurs as Treub thought, and my reasons are as follows: 
1. The cases of fertilization observed (figs. 20, 21) show no 
endosperm. 
2. The pollen tube sometimes enters the ovule before the 
embryo sacs are ready for fertilization. In one case pollen 
