1918] OTTLEY—IMPATIENS 307 
nucleoli possess one or more vacuoles. What appears to be a later 
stage in the fusion of the two polars is given in fig. 43. A dense 
granular mass, the entering nucleolus, seems to be in vital contact 
with the nucleolus of the receiving nucleus and gives the impres- 
sion of giving of its substance to help in the formation of the 
nucleolus of the resulting endosperm nucleus. The characteris- 
tically large vacuole of the primary endosperm nucleolus has 
already appeared. Not all of the entering nucleolus fuses with 
the receiving nucleolus, however, for coarse strands radiate out 
from the dense mass of nucleolar substance and appear to be adding 
to the reticulum of the nucleoplasm. A similar radiating mass has 
been observed in one of two polars. In this case it might represent 
a stage in the fusion of the second sperm with one of the polars 
before the two polar nuclei had united. Similar masses have also 
been seen in the megaspore mother cell, and here also the nucleolus 
doubtless contributes to the chromatic substance. 
The fusion of the two polars has been figured by numer- 
ous writers for many different plants. In Nicotiana Tabacum 
(GUIGNARD 23) the two nucleoli remain distinct in the fusion nu- 
cleus for some time before fusing. VANDENDRIES (44) figures for 
Cardamine pratensis two nucleoli within the primary endosperm 
nucleus with a sperm against one side of it. He says that when the 
pollen tube enters the cavity of the embryo sac the two polar nuclei 
have begun to fuse but the nucleoli are still distinct. In J. Sultani, 
however, the fusion of the two polar nuclei begins relatively much 
later and takes place very quickly. In describing the fusion of the 
two polars of Arisaema triphyllum, Gow (18) says that the fusion 
endosperm nucleus frequently contains two nucleoli. 
It seems highly probable that after the primary endosperm 
nucleus is formed the second sperm unites with it. By this time 
the sperm nucleus appears to be larger than it was in earlier stages. 
In fig. 44 it is just at the point of piercing the nuclear membrane, 
and in fig. 45 it is within the primary endosperm nucleus and lying 
either above its nucleolus or within it. It was impossible to deter- 
mine if the second sperm, in all cases, waited until the primary 
endosperm nucleus was formed before becoming functional. 
GUIGNARD (23) is convinced that in the Malvaceae the time of 
