1900 | SPOROPHYLLS AND SPORANGIA OF ISOETES 253 
Quite often, too, it happens that one cell gets the advantage 
almost from the beginning. But it may be stated as the rule 
that there is a selection and partial enlargement of many more 
cells than can ultimately become mother cells, and these enlarg- 
ing cells belong mostly to the third and fourth layers of the 
sporangium, either extending continuously across the sporan- 
gium or occurring in groups separated by ordinary. cells. That 
this condition is associated with the selection of megaspore 
mother cells is proved, I think, by the fact that enlarging cells, 
comparable to those of fig. 63, are never found in the sporangia 
formed late in the season, that is, in those which are to bear 
microspores. 
What becomes of the defeated cells? This is a difficult ques- 
tion to answer, for since there is so, much variation in the early 
condition of the megasporangium it is impossible when examin- 
ing one of the later stages to tell just what the antecedent con- 
ditions in that sporangium may have been. From the frequency 
with which karyokinetic figures appear in the cells surrounding 
the nearly mature megaspore mother cells, it seems pretty cer- 
tain that the cells which have been left behind in the struggle 
simply divide until their products have the general size and 
appearance of the other cells of the sporangium. If the enlarge- 
ment has not gone very far the cells retain their angular con- 
figuration; if it has gone further the cells may round up while 
exerting a considerable pressure on those adjacent. Sol inter- 
pret the group ¢ in fig. 67. 
Fig. 66 will furnish a good illustration of the behavior of the 
unsuccessful mother cells, although no single section can be so 
convincing as a series of them. The tissues are somewhat con- 
tracted, but this defect does not hide the rounded form of cer- 
tain groups of cells, and their marked resemblance, except in 
being multicellular, to the mother cells. The section contains 
but one fertile mother cell, the one labeled ™. One other 1s 
situated in the opposite end of the sporangium, just beyond the 
limit of the figure. The cell a is undergoing division, the mitotic 
figure being seen in the adjacent section. An interesting fact 
