534 Thomas.—Double Fertilization in a 
definitive nucleus takes place before that of the other with the 
oosphere (/. c. f Fig. i, B). 
The spermatozoids of Rudbeckia , and also of Helianthus , 
show the characteristic shape and granular structure extremely 
well. In Helianthus they are very long and twisted like a 
corkscrew, while they are shorter and thicker in Rudbeckia , 
but show their structure even better. 
Nawaschin differs from Guignard in not having seen the 
spermatozoids of L ilium either homogeneous or with a spiral 
ribbon at any period. In Caltha they are so extremely small, 
when they first come from the pollen-tube, and take the stain 
so heavily, that I was not able to make out any structure 
whatever. They appeared homogeneous, but this may have 
been due to difficulties in observation. Later, when the one 
spermatozoid has reached the definitive nucleus, it is immensely 
swollen, and has a particularly light, spongy structure with 
minute scattered granules. 
Professor Nawaschin has also made discoveries of the utmost 
importance in Orchids. These plants form no endosperm, 
and it is therefore of great theoretical significance to find 
that, even when the embryo has attained a considerable size, 
the three nuclei associated together in the centre of the sac 
have not coalesced. Two of these are the unfused polar 
nuclei, and there can be little doubt that the third is a 
spermatozoid, although it has lost its characteristic form 
(/. c., Fig. 2). 
Professor Nawaschin has always believed that the fusion 
of the second male generative nucleus with the definitive 
nucleus is a true fertilization, and he takes these results as 
in a great measure proving it. For our knowledge of the 
nature of true fertilization is so limited that at present we 
can say little more than that it is followed by division. And 
in this respect the result of the two fusions is identical. 
I have also read Professor Guignard’s paper on Tulips, in 
which he mentions that he has seen the double fertilization 
in some Dicotyledons, including Ranunculaceae. 
