Nov., 1907.] 
Life History of Cornus Florida. 
1 99 
in turn divided until there are four parietals, and at least two 
radial sporogenous layers. 
Material collected August 26th showed that in the youngest 
flowers the three outer parietal layers remain thin and flat while 
the inner has enlarged and functions as the tapetum. The 
sporogenous tissue has reached the microsporocyte stage, the 
nuclei being in synizesis (Fig. 8). Very commonly the chromatin 
is in a contracted mass on one side of the nuclear cavity while the 
nucleolus lies free on the other side. 
In the oldest flowers of this date the tapetal layer is much 
broken up into individual cells which are binucleate. The 
microsporocytes have divided twice in rapid succession without 
forming a cell wall between them. The result is the spore 
tetrad within the microsporocyte wall (Fig. 9). 
On September 2d the cells of the tetrad had separated into 
the individual spores. The microspores are somewhat elongated 
with three double ridges upon their surface. 
Commencing September the Sth a gelatinous mass is forming 
within the microsporangia. On September 24th it had grown 
much more dense and on the 26th of the same month of the 
previous year the same condition was present. As this matrix 
(Fig. 12) remains within the sporangia throughout the winter it 
no doubt functions as a protection to the microspores and pollen 
grains. In the spring it begins to dissolve in some sporangia the 
last of February while in others it remains until the last of April. 
At just what date the microspores divide to form the two- 
celled pollen grain (male gametophyte) was difficult to determine 
because of the deep stain which the gelatinous matrix takes. It 
was found, however, that the two-celled stage was present 
December 4th. In this stage, then, they pass the winter, the 
male gametophyte being developed the fall previous to the 
blooming of the flower. 
THE DEVELOPMENT OF THE FEMALE GAMETOPHYTE. 
As has been stated, the incipient ovule makes its appearance 
about August 11th as a papilla on the wall of'the stylar canal. 
It grows downward and then bends upon itself becoming anatro- 
pus August 18th. On this same date the single integument 
makes its appearance. On August 18th, less than one month 
after the appearance of the first floral organs, the sepals, the 
hvpodermal archesporial cell is much elongated and contains a 
large nucleus. This cell becomes the megasporoevte (Fig. 14). 
One week later, August 26th, two subsequent cell divisions 
have occurred. The result is the four megaspores (Fig. 15). Of 
these the three apical ones are small and non-functional, while 
the other, functional one is five or six times as large. No cell 
walls were seen between them. 
