Discoid gemmae in Radula 
RUTH WILLISTON 
Discoid gemmae, borne on the margins or surface of the leaves 
or on the thallus, have been reported in the following twelve 
genera of the Jungermanniales: Metzgeria, Radula, Porella, Mets- 
geriopsis, Colurolejeunea, Diplasiolejeunea, Cololejeunea, Lepto- 
colea, Aphanolejeunea, Lejeunea, Cyclolejeunea, and Frullania. 
(See Evans, ’o4, ’10, and 11.) It is probable, however, that they 
occur in others. In Radula they are definitely known in only 
seven species, although the genus, according to Stephani (‘10), 
contains 220 species in all. In two species, R. Hedingert and R. 
iibodensis, the development of the gemmae has been carefully 
studied by Goebel (87). A third species, R. complanata, was 
investigated by Cavers ('03) and later by Stevens (’10). In R. 
ccida gemmae were observed by Gottsche (’63), in R. Lind- 
bergiana by Jack (’81), in R. protensa by Schiffner (’93), and 
he R. subtropica by the writer; but no details about the gemmae 
in these four species have as yet been published. The present 
Paper will be largely devoted to the gemmae of R. flaccida and R. 
Protensa, although the other species will be included in the dis- 
Cussion, 
RADULA FLACCIDA 
. This species was first described from Mexico in 1847 by 
Lindenberg and Gottsche (Syn. Hepat. 726). It has since been 
found widely distributed throughout the West Indies and the low- 
lands of tropical America. The material used in this study was 
collected by Dr. A. W. Evans at Bath, Jamaica (no. 332). R. 
tda is a dioecious species with a prostrate stem. It is epiphyl- 
lous. The gemmae are disklike bodies, one cell thick, attached 
to the dorsal margins of the leaves. They are the largest and 
most highly differentiated gemmae known in the genus, averaging 
ie Maturity o.5 mm. in diameter, while the leaves themselves 
measure only 0,8 mm. in length. The cells nearest the center of 
the se€mmae are the largest, averaging 0.02 mm. in diameter. 
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