ALDEN: LIFE HISTORY OF UVULARIA SESSILIFOLIA 443 
The material collected October 21, 1910, and that collected 
October 27, 1909, show the formation of tetrads, the phases varying 
from the equatorial plate stage of the heterotypic division to the 
complete organization of the four daughter nuclei. The usual 
large thick chromosomes that characterize the reducing division 
are seen. At the end of this division a resting nucleus is formed 
in each of the daughter cells, but no wall separates the two. The 
homoeotypic division, however, is not long delayed, as in the same 
anther all these stages may be found including the completed 
tetrads. 
The spores round off and increase in size; it is at this point 
that the approach of winter is met. With the renewal of growth 
in the spring the pollen grains found in early March show the outer 
and inner walls differentiated and apparently mature in size. In 
this early spring condition the nucleolus is prominent, and the 
linin mesh fine and close with small chromatic granules. The divi- 
sion of the pollen grain nucleus into tube and generative nuclei 
is noted in the late April material, in which the generative nucleus 
appears not fully organized but showing traces of the spireme 
condition, and the tube nucleus is characterized by a large 
nucleolus but poorly organized reticulum, FIG. 8. The genera- 
tive nucleus is rich in chromatic material staining deeply, and the 
tube nucleus has but little. I have not found the division of 
the generative nucleus, which evidently takes place after the 
shedding of the pollen. 
DEVELOPMENT OF THE MEGASPORANGIUM 
Turning to the study of the megasporangium, we find that its 
development is as tardy as that of the microsporangium is early. 
t the time when the archesporium of the microsporangium is 
formed, the ovary is a homogeneous mass. In September the 
Carpelary cavities have appeared, and in each a pair of nucelli 
are protruding. The number of these cell masses destined to 
develop the megasporangia varies from two to three pairs for 
€ach cavity. In general each of a pair is on the same plane. In 
October and evens late as December the uniformity of the nucellar 
tissue is unchanged, and very little change in size is noted, FIG. 9 
and io, In early March the outline of the nucellus is such as to 
