532 Thomas.—Double Fertilization in a 
not begun, so that we can follow its shape from end to end. 
It makes one large coil almost back upon itself, by means of 
which it rises on to the surface of the definitive nucleus. 
I have seen a great many other sacs, in which it was 
perfectly evident that the second fertilization had taken place, 
but fusion had gone too far for one to be able to distinguish 
the vermiform nucleus with precision. 
It will be noticed in the illustrations that I have given 
that the definitive nucleus does not present a rounded, even 
contour, but that it often appears as if the polar nuclei of 
which it is composed still retain their individuality to some 
extent. This is most marked in the fusion shown in Fig. 4, 
where the definitive nucleus still contains several nucleoli, 
and at one side the polar nuclei are quite separate. The 
definitive nuclei shown in Figs. 7 and 9 contain only one 
nucleolus, but there are deep indentations in their outlines 
which probably mark the boundaries of their component 
nuclei. This seems at first a little difficult to reconcile with 
the very numerous instances I have seen of one large, almost 
perfectly round, definitive nucleus, in sacs not yet fertilized. 
It is quite possible that some at any rate of these have passed 
the stage at which fertilization is possible, and that they then 
fully complete their earlier fusion. Some, however, certainly 
do unite completely, before fertilization, for I have seen a 
vermiform nucleus fusing with a single large definitive nucleus 
containing one central nucleolus. 
The synergids also differ somewhat in their condition at 
the time of the entrance of the pollen-tube. Generally they 
seem fairly round and healthy, but very soon become dis¬ 
organized. Sometimes they possess a somewhat broken 
outline, even when the pollen-tube first enters. 
The antipodals, on the contrary, remain large and important¬ 
looking after fertilization has taken place, as Dr. Westermaier 1 
has found to be the case in many members of the order 
Ranunculaceae. 
1 Dr. M. Westermaier, Zur Embryologie der Phanerogamen, insbesondere iiber die 
sogenannten Antipoden. Halle (Acad. Leop.), 1890. 
