472 Stevens . — Spore Formation in Botrychmm virginianum, 
layer becomes as much as four or five cells in thickness, while I find two 
cells in thickness the rule. His material shows an excessive growth of the 
tapetum about the time of the first prophase and after, while mine does not. 
I have measured the volume of the tapetum before it begins to flow in 
between the groups of spore-mother-cells, and find it more than two-thirds 
the volume of the sporogenous tissue ; and since the sporangia do not 
essentially increase in size while the inflow is taking place, this amount is 
evidently sufficient to fill the gaps between the groups and still leave the 
thin layer that remains at the exterior. He finds frequent amitotic nuclear 
division in the tapetum, while my material does not show this. Our sub- 
jects agree in showing that none of the spore-mother-cells is restrained 
from forming spores. 
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