Bh eens 
, oe "7 
1897 | THE LIFE HISTORY OF SAGITTARIA VARIABILIS 255 
even at this early stage, before the conjugation of the polar 
nuclei and the act of fertilization, they are often cut off by well 
defined cell walls (fig. zz). 
In approaching each other the upper larger polar nucleus 
travels much farther than the lower one, so that the place of 
contact is usually in the lower part of the embryo sac (figs. rg, 
79,25), and the fusion takes place here without any apparent 
shifting of the nuclei, the fusion being usually complete before 
the entrance of the pollen tube into the sac (fig. 79). Frequently 
two centrosomes with a common hyaline area around them can be 
seen on one or both sides of the conjugating nuclei (fg. 73), 
indicating a possible union of the two pairs of centrospheres 
which are brought together when the two nuclei approach each 
other. Later the appearance is as though the two centrosomes 
had fused (jigs. 75, 76). Although these observations were not 
very extensive, they agree with what I observed in the conju- 
gating polar nuclei of A/isma Plantago. There is usually one 
large nucleolus in each polar nucleus, and during the fusion of 
the polar nuclei their nucleoli also seemed to fuse. When the 
nuclear fusion is nearly complete, two or three nucleoli appear 
close together (figs. 75, 76), and a little later the nucleoli are 
seen to lie in contact (figs.77, 78). When nuclear fusion is 
completed, the definitive nucleus nearly always shows but one 
large nucleolus (figs. 79, 29), so there can be but little doubt 
from the stages observed that the nucleoli come together and 
fuse directly as definite bodies, without breaking up or being 
dissolved. 
plmeamire caccig eg OF FERTILIZATI ON. 
Just before the entrance of the pollen tube into the micro- : 
pyle, the two synergids lie side by side, with the oosphere 
Suspended below and lying somewhat to one side (figs. 74, 79, 20). 
In the lower part of each synergid there is a large vacuole. 
_ At this stage the nucleus of the oosphere is woually: —, - 
_ ‘Metrical, being spherical or ellipsoidal in shape. _ 
Tt mt be remembered that the pollen gain hae the two 
