336 WILLISTON: DISCOID GEMMAE IN RADULA 
respond to those described by Leitgeb (’79) for the vegetative 
shoots of R. complanata, the cell cutting off segments on three 
sides only. The fourth face, which does not cut off segments, is 
the free one of the apical cell and lies toward the apex of the 
branch. Each segment cut off by a lateral face divides into two 
cells, an external cell and an internal cell. The external cell gives 
rise to the two lobes of the leaf and the cortical cells of the stem, 
while the internal cell by further division forms the axial cells of the 
stem. The segments cut off by the ventral face never form leaves 
but give rise to cells of the stem only. The three faces of the 
apical cell cut off their segments in spiral sequence, but the spiral 
may be either dextrorse or sinistrorse (FIG. 25 and 26). 
RADULA PROTENSA 
Lindenberg first described R. protensa from Java in 1848 
: (Meissner, p. 462). It is a tropical species native to Asia and 
various islands of the Pacific. The material used in this study 
was collected by Lamberto Loria in New Guinea (no. 114). &. 
protensa agrees with R. flaccida in being epiphyllous and prostrate. 
The gemmae are smaller than in R. flaccida, averaging only 0.2 
mm. in diameter at time of shedding. It is possible, however, 
that the gemmae examined@had not attained their full size, 2 
spite of the fact that cell division had apparently ceased. In this 
species gemmae occur on vegetative branches and on male bracts. 
Schiffner (’93, p. 249) reports them also on the margins of old 
perianths. They are most commonly found scattered over the 
ventral surface of the leaves or along the margins and stand at 
right angles to the surface. They usually appear in groups, 4 
single leaf sometimes bearing fifty or more in various stages of 
development. 
As in R. flaccida the development of the gemma begins by es 
protrusion of an ordinary leaf cell. This cell, however, unlike 
that of R. flaccida, may occur in the surface of the leaf or in the 
margin. It also becomes covered with a much heavier covering 
of gelatinous material than is found in R. flaccida. The Or. 
half of the cell is then cut off by a transverse wall. This — 
forms the stalk cell, which does not project beyond the surface 0 
the leaf, and the gemma mother cell, which soon divides into 
