WILLISTON: Discomp GEMMAE IN RADULA 335 
(FIG. 18 and 19). If the growth and division of the neighboring 
cells are very rapid, the large cell may appear in a temporary 
depression, but it soon increases in size so that the mature gemma 
shows no marginal indentations (FIG. 23), 
After the large cells are fully differentiated, the gemma is shed. 
Shedding takes place by means of a splitting between the stalk 
cell and the long basal cells (Fic. 16). This splitting is probably 
caused by a gelatinization of the walls in this region. The stalk 
cell does not come off with the gemma, as it does in R. complanata, 
but remains a part of the leaf, as in the two species studied by 
Goebel (’87, f.61). Cell divisions are now at an end until germina- 
tion takes place, but the gemma may increase slightly in size by 
the enlargement of its individual cells. When mature it is a 
slightly concave disk with a { unnellike outgrowth near the center 
and with the six large basal cells often adhering to the edge of the 
funnel, 
All the germinating gemmae in this material were found on the 
lower surface of the leaves on which the plants were growing. It 
Seemed remarkable that the spaces on the upper surface of the 
leaves were entirely free from isolated gemmae or young plants. 
After a gemma comes to rest with its concave side down, the first 
step in germination is the formatién of rhizoids to anchor the 
young plant. These are developed from the cells near the peri- 
Phery where the tissue comes in contact with the substratum. 
The rhizoids consist of short prolongations of the cells, with ir- 
regular lobes at the apex. According to Goebel (87, p. 53, f- 66) 
the similar thizoids in R. Hedingeri probably secrete a gelatinous 
Substance by means of which they adhere to the substratum. 
When the gemma is firmly anchored, the five large peripheral 
cells (FIG. 19) begin to divide (FIG. 20-23). The first wall 
'S always Periclinal, and the inner cell thus formed gives rise to 
the young shoot. The outer cell, as well as the neighboring cells, 
Proceeds to divide and form a tissue which protrudes beyond the 
"Bin of the gemma (FIG. 20). This thalluslike body protects 
the tiny shoot coming out on the ventral side of the concave 
gemma, The sequence of divisions in the inner cell of the original 
Peripheral cell is very complicated and difficult to follow; but 
4 tetrahedral apical cell is soon formed, the divisions of which cor- 
