WILLISTON: DISCOID GEMMAE IN RADULA 337 
quadrants. The early walls are very delicate and scarcely show 
through the surrounding gelatinous layer. As the gemma increases 
in size it breaks through this sheath, which remains clinging to 
the base like a collar (FIG. 30). In the further development of the 
gemma the two apical quadrants function for a time as two-sided 
apical cells. As described for R. flaccida, the stage at which the 
apical cell becomes established and the stage at which it ceases to 
function vary. There is no curving or change in position in this 
gemma as is noted in R. flaccida; and at the time of shedding, the 
gemma is a circular body, one cell thick, slightly concave, but 
without any funnel-shaped outgrowth similar to that of R. flaccida 
Ficures 30-37, Radula protensa. Stages in development of gemma from the 
Wo-celled stage until the apical cell ceases to function, X 400. 30-32 show the stalk 
cell and the gelatinous sheath. 
(Fic. 14). Shedding takes place by means of a splitting of the 
wall between the stalk cell and the basal cells. The stalk cell 
femains as a part of the leaf. The form of the gemma when shed is 
almost identical with that of the mature gemma of R. Hedingert. 
Soon after shedding, the basal cells begin to elongate. On account 
of lack of germinating material it was impossible to trace the 
further development of the gemma. However, a few gemmae were 
found in which the marginal cells halfway between the basal cells 
and the apex, on one side or the other, were dividing and growing, 
“Pparently beginning to form a thalluslike outgrowth. So far as 
Could be determined, there were no enlarged cells functioning as 
