+t ee ee ees 
1896. ] Embryo-sac of Alisma. 131 
7. The centrospheres of the lower sperm nucleus precede 
it as it approaches the oosphere. 
€ nucleus of the oosphere becomes bulged out on the 
side nearest the sperm nucleus, and its centrospheres being 
situated immediately opposite this bulge, travel slightly to- 
ward the approaching male nucleus. 
9. All the stages preliminary to the conjugation of the male 
and female nuclei are favorable to, and indicate a conjugation 
of their centrospheres, at the time of impregnation of the 
oosphere. 
10, After the first division of the oospore, in the develop- 
ment of the proembryo, the three succeeding divisions take 
place each time in the outermost cell, the first three divisions 
being transverse to the long axis of the embryo-sac, the 
fourth one longitudinal. 
Ann Arbor, Michigan. 
EXPLANATION oF PLates IX anp X. 
Fi 
ig.1. A young nucellus with macrospore and remains of the tape- 
tal cell at the upper end. 
Fig. 2. Mature embryo-sac with eight nucl 
el. 
Fig. 3. Two polar nuclei just before conjugation, showing the cen- 
TOospheres Joining in couples. i 
fuseg, 4, COnjugation of polar nuclei; the ae 
here Centrosomes lie close together in the united attraction- 
: Ig. 5. Conjugation of polar nuclei; the larger nucleus is from the 
Pper end of the emb 0-sac 
two prominent centrospheres. f 
i bryo-sac with oospore dividing, and with endosperm cells. 
ee Pollen-grain with a large and a small nucleus. — 
Fig re: Pollen-grain, showing the small nucleus in stage of — 
farthe: = Pollen-grain with the division of the generative nucleus 
€t advanced 
Bg 2 Mature in wi all nuclei. 
ig. ro € pollen-grain with one large and two sm 
rho 13° Upper end of ee embryo-sac, showing the ap “gig 
this 5 2ugating Sperm-nucleus after leaving the pollen-tube. 4 
Perm-nucleus is the oosphere, while at the apex of the sac is the 
Mucleys &5Y"ergida, and at the left of the latter is the second sperm- 
i vy ot the Pollen-tube ‘ 
thas :* Outer end of the ovule, showing the pollen-tube passing 
80 the Micropyle and into the embryo-sac. 
