1900] LIFE HISTORY OF QUERCUS 413 
upon the equatorial plane. The number and form of the chro- 
mosomes are so markedly different from those of the vegetative 
cell that they afford conclusive evidence that the divisions are of 
the reduction type, and in view of all the circumstances it can 
scarcely be doubted that it is the first division in fertile mega- 
spores. In fig. 3z we have a case in which two adjacent mega- 
spores have reached the four-celled stage. Considering the large 
number of archesporial cells, and the frequency with which a 
number of these undergo early mitotic phases, it has been a 
matter of surprise that the phenomenon of a two-celled stage or 
a four-celled stage in more than one megaspore in the same 
nucellus does not more frequently occur. This condition, how- 
ever, we may better appreciate when we have learned more of 
the causes which determine the fate of a cell. 
The first division observed in the apical region of any mature 
nucellus is shown in figs. 26 and 27. This is believed to be the 
spirem stage of the first division of the megaspore. The thread 
is small and I am unable to determine whether or not it conforms 
to the mode of splitting commonly ascribed to spore mother 
cells. Whatever weight, however, may be attached to synapsis 
as restricted to such division obtains here. Material collected 
June 4 and 5 afforded many cases of the fertile megaspore 
presenting phases illustrated in figs. 27-27. The transition to 
the four-celled stage of the embryo sac is accomplished with 
speed and marked uniformity of time in all the ovules. Mate-_ 
rial collected June 5 showed early phases up to and including 
the spirem stage of the first division of the megaspore to be 
quite common ( figs. 27-25), while material collected two days 
later showed the four-celled stage of the sac with corresponding 
frequency. 
Notwithstanding a large number of ovules in which the two- 
celled stage might be sought were sectioned, fig. 28 probably 
illustrates the most satisfactory case of a two-nucleated sac. It 
shows two deeply stained masses which I take to be the 
two unorganized daughter nuclei of the first division of the 
megaspore, and in no case did I find two nuclei in the so-called 
resting stage. 
