36 MARCUS M. HARTOG. 
2. Angiosperms. 
In AncriosperMs the processes in the pollen-tube show 
a still further degeneration. The original nucleus divides 
into two: (1) a vegetative nucleus corresponding to the 
multicellular body of the Gymnosperms; (2) a reproductive 
nucleus corresponding to the gametogonial nucleus of that 
group: but no cellulose wall separates them; or if a rudi- 
mentary cell-wall be formed, it is at once absorbed. The 
vegetative nucleus seems here to have a function in con- 
nection with the growth of the pollen-tube, at the apex of 
which it lies, degenerating when this growth is completed. 
The gametogonial or generative nucleus then passes forward 
into the apex of the tube and undergoes mitosis; one of the 
two nuclei so formed is the male pronucleus, and passes into 
the oosphere.! 
Here we have the two mitoses demanded by popular theory, 
but an interval of hours or days separates their occurrence ; 
and the morphological explanation—that the first differen- 
tiates a prothalliar from a gametogonial nucleus, and that the 
second (of the latter only) is a gametogenic fission—is abso- 
lutely incontrovertible, when we compare the pollen-grain here 
with that of Gymnosperms, and again with the androspores of 
Heterosporous Cryptogams. 
The FEMALE GAMETE is differentiated in the embryo-sac by 
a process unrivalled in complexity ; while the morphology of 
the process is still doubtful. In recapitulating this, I will try 
by full notation to make the relations and fates of the nuclei 
as clear as possible. The embryo-sac corresponds to that of 
Gymnosperms, and most morphologists are agreed in regard- 
ing it as a megaspore, homologous with those of the Hetero- 
sporous Filicines that develop into a reduced prothallus 
bearing few archegonia only. Three mitotic divisions of its 
1 Strasbirger and Elfving, who first discovered this process, originally 
reversed the parts of the respective nuclei. In some cases the generative 
nucleus undergoes two mitoses and so forms four gametonuclei. 
