Dicotyledon—Caltha palustris . 533 
The definitive nucleus divides by mitosis, and often forms 
a considerable amount of endosperm before the oosphere 
divides. The first wall formed in the latter is at right angles 
to the long axis of the sac. 
All the practical work in connexion with this paper was 
done at the Royal College of Science last summer, but 
although I was convinced that a double fertilization, by 
means of vermiform nuclei from the pollen-tube, took place, 
I was unwilling to publish at the time, as I had not found 
a perfect and unmistakable fertilization of the oosphere by 
the male nucleus, in the same sac with the fertilization of 
the definitive nucleus. In examining my slides again this 
spring, however, I came across a perfectly satisfactory fusion 
of the oosphere and male nucleus previously overlooked (see 
Figs. % and 5). In the same sac is a sufficiently good polar 
fertilization, although only a small portion of the vermiform 
nucleus is to be seen, but, as I explained before, it seems 
unlikely that an equally felicitous stage of both will be found 
in the same sac. 
My thanks are due to Miss Sargant for very kindly giving 
me her advice on some slides that I submitted to her. 
Since writing this paper, I have seen Professor Nawaschin’s 
recently issued account of double fertilization in Dicotyledons. 
As a representative of the Ranunculaceae he has examined 
Delphinium , and although not able to find the male generative, 
nuclei free in the embryo-sac, he saw them as vermiform 
structures in the pollen-tube, and again when fusing with the 
nucleus of the oosphere and definitive nucleus respectively. In 
two respects Delphinium resembles Caltha\ its polar nuclei unite 
before fertilization, and the fertilized ovum remains undivided 
for a considerable time. There are no figures of this plant. 
Professor Nawaschin’s paper is, however, more particularly 
concerned with two Composites, Helianthus annum and Ritd- 
beckia speciosa. In both these plants also, the polar nuclei 
coalesce before fertilization. In Rudbeckia , as I found in 
Caltha , the fusion of the one male generative nucleus with the 
