334 WILLISTON: DIscoID GEMMAE IN RADULA 
the beginning, each cell dividing by longitudinal walls followed 
by transverse walls; but as the gemma grows older the order 
of cell division is reversed, and the transverse walls are formed 
first and the longitudinal later. 
In R, Hedingeri Goebel reports (’87, p. 52) that there are no 
apical cells whatever, and the gemma mother cell divides by a 
series of longitudinal walls between which transverse walls are 
formed. 
Soon after the apical cells cease to function, the gemma begins 
to change its position and shape. Up to this time it has been a 
flat circular body protruding by the stalk cell beyond the margin 
of the leaf. Now the six or eight basal cells which attach the 
28 
FIGURES 27-209, Radula flaccida. 27, gemma at maturity, ventral view, — 
the large marginal cells and the basal cells, X66. 28, germinating gemma showing 
one leafy shoot more advanced than the others, X266. 29, germinating ants 
later stage, with a well-developed leafy shoot, * 266. 
gemma to the stalk begin to grow, especially in length, and curve 
upwards so that they stand at right angles to the leaf. As = 
change in position takes place the cells adjacent to the large basa 
cells begin to divide and grow very rapidly, and to curve outward 
in such a way that the gemma again becomes parallel with the 
leaf surface but raised above it by a funnel-shaped tube. A oo 
time before the gemma is mature several large cells becom® 
differentiated at intervals along the margin (FIG. 27). These soe 
in number from three to eight, but there are usually five. ae 
one arises through the enlargement of one of the peripheral & alls 
while the adjoining peripheral cells divide by periclinal w 
