252 BOTANICAL GAZETTE [APRIL 
the mother cells. But that explanation being precluded it 
became necessary to determine their relation to the single large 
mother cells, and to learn their later and earlier history. In 
attempting to do so I have become convinced that a very large 
number of cells are potentially megaspore mother cells, that a 
considerable number of these make a start to differentiate them- 
selves fully from the sterile cells, but that comparatively few 
are finally successful in reaching the large size and well-nour- 
ished condition necessary for the production of megaspores. 
The changes which first distinguish the megasporangium 
occur relatively earlier than those which mark the microsporan- 
gium. In the latter, as we have seen, the first change is the 
separation of certain sterile regions from the fertile cells as indi- 
cated by a difference in cell contents. In the former, however, ~ 
changes occur at a considerable time before there is any possibil- 
ity of distinguishing the trabecule. When the megasporangium 
has reached a stage of development considerably more advanced 
than that shown in fig. 43, a change is discernible in many of the 
cells which form the third and fourth layers approximately. 
The whole sporangium has at this time entered upon the period 
of enlargement due to the growth of the individual cells. But 
in fig. 63 it is clear that certain cells have greatly outgrown 
their fellows. Their well-nourished condition is attested by the 
density of their cytoplasm and their large nuclei, which contain 
many nucleoli. All these enlarged cells are engaged in the 
struggle to become mother cells. Which and how many will be 
successful will probably depend upon their holding an advan- 
tageous position with respect to the supply of nutriment, pet 
haps also to their having obtained an earlier start. 
It does not always happen that a considerable group of cells 
enlarge together. Indeed, it is a comparatively rare case when 
all the cells of the third and fourth layers enlarge to any con- 
siderable extent. Sometimes the enlarging cells are in more * 
less isolated groups separated by cells of ordinary size. fig. 
64 shows such a group of cells, taken from the side of a Sp 
rangium., ! 
