108 BOTANICAL GAZETTE [AUGUST 
notwithstanding the presence of an antipodal prolongation, is 
‘explained. Thus I bélieve we have the solution of the antipodal 
problem in Casuarina. Some of the antipodal prolongations 
grow so long that they penetrate the chalaza, occasionally pas- 
sing slightly beyond it into the funiculus. 
The location of the polar nuclei is quite various. Like the 
antipodals, they seem occasionally to pass into the antipodal 
prolongations (figs. rg D, 77), and are lost in the maze of tubes. 
Sometimes only one was found (fig. 76, ¢), but in this case the 
polars may have fused and this is the endosperm nucleus. The 
sac then, except for the antipodal prolongation and its conse- 
quent effect upon the location of the antipodals and the endo- 
sperm nucleus, seems to be normal in its development. 
Only one pollen tube penetrates a flower, hence only one 
ovule is entered and only one embryo sac in that ovule is fertil- 
ized. The favored sac was in all the observed cases near the 
micropylar end of the megaspore group. The pollen tube enters 
the ovule as Treub has stated (5). Coming down the central 
placenta (jig. 78), it wanders somewhat in the region where the 
funiculus has its origin, as though the attractive influence, of 
whatever it is that guides it, were not sufficiently strong to guide 
it with certainty. The tubes again frequently branch just before 
entering the chalaza (fig. 78,6). Sometimes the branches reach 
the surface, as Treub says, and he suggests two possible reasons 
for the branching: (a) for aeration; this is suggested by their 
often reaching the surface; (6) for holdfasts to anchor the tube 
firmly before it makes its entry into the nucellus. Neither of 
these appeals to me very strongly, and for the latter I see no 
reason at all. The cause is probably the same as that which 
causes wandering at the point of entry into the funiculus. 
The tube seems to enter the prolongation of one of the 
embryo sacs and thus finds an easy passage through the chalaza. 
The plugs of cellulose in the tubes at intervals, as reported by 
Treub, are quite rare in C. stricta, and when present are short, 
resembling more a thick transverse wall than a plug. In the 
maze of tubular antipodal prolongations I was not able to follow 
the pollen tubes with certainty, and cannot therefore say whether 
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— eee 
