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254 BOTANICAL GAZETTE | APRIL 
which goes far to explain the division of the groups 4, 4, is the 
occurrence in adjacent sections of larger undivided cells (fertile 
mother cells), similar to m, and so situated as to be almost or 
quite in contact with the dividing groups. Their proximity 
accounts for the failure of the groups 4, J, to produce spores. 
Some of the smaller and less rounded groups probably repre- 
sent mother cells which suffered an early defeat, while the 
larger groups represent those which held out almost to the last. 
Such cases as these, which can be easily duplicated in rapidly 
growing sporangia of the right age, are conclusive, it seems to 
me, when considered in conjunction with the manner of growth 
of the sporangium, to show that the fertile mother cells are 
selected by their advantageous environment and not by any 
strict morphological position. 
The fertile mother cells increase enormously in size before 
dividing into spores, Their nuclei maintain a proportionate 
growth, and their cytoplasm remains dense though not homog- 
eneous, and frequently contains grains of starchy matter and 
drops of oil. 
Notwithstanding the large size of the mother cells and of 
their nuclei I was unable to make any detailed study of their 
division. About the time when division occurs, the cells seem 
to be peculiarly liable to suffer plasmolysis, for under the action 
of the fixing agent they are contracted to a mere fraction of 
their proper volume. When sectioned in this condition they are 
seen to lie free in large cavities which presumably they filled 
completely when living, and they stain so intensely that it is 
impossible to make out any details of the karyokinetic process. 
I have not once had the good fortune to see karyokinesis in an 
uncontracted megaspore mother cell, although the corresponding 
phase of the microsporangium offers no technical obstructions 
to cytological study. The liability of the megaspore mother 
cells to suffer contraction in the process of fixation was noticed 
by Kienitz-Gerloff (1) and other investigators; it is possibly 
associated with the entrance of the nuclei into the synapsis 
Stage. 
