174 BOTANICAL GAZETTE (MARCH 
ments (fig. rz), and the prothallium then is very like a young pro- 
thallium of Hymenophyllum or Trichomanes. 
Even before the relation of these three cells is clear, division of the 
larger prothallial cell by a transverse wall has usually taken place 
(fig. 10). Development now proceeds in one of three ways: (a) 
longitudinal and transverse wall formation may follow so as to pro- 
duce two rows of nearly equal cells (jigs. 13, 14, 15); (6) an oblique . 
wall may take the place of the first longitudinal wall so that, almost 
from the first, growth is by an apical cell cutting off segments right 
and left (figs. 16, 77); (c) the longitudinal walls may not come in at 
all, and a filament of a single row of cells is produced (jig. 78). The 
last case seems to be comparatively rare; the others appear about 
equally often. 
This course of development may be altered by varying the con- 
ditions in which the prothallia grow. Under a screen of potassium 
bichromate solution, and in both weak and strong sunlight, filaments 
of a single row of cells were produced, and these did not broaden 
toa thallus. The filaments sometimes reached a length of 4 or 5™™, 
attaining this not through numerous divisions, but by the very unusual 
length of many of the cells. The small cell between the rhizoid and 
the first prothallial cell was present in these filaments. 
In none of these cultures did antheridia appear, though some of 
them were kept for a time longer than that within which antheridia 
are produced under usual conditions. The early appearance of 
antheridia on filamentous prothallia has been reported as usual. 
WoRONEW (17), however, says that he failed to get antheridia on 
filaments growing in weaker light, but was able to bring about their 
early production by unfavorable conditions of crowding, drying, etc. 
In a culture growing in dirt badly overrun by algae, I did find a 
few prothallia with antheridia produced from the third or fourth 
cell. 
Under a screen of ammoniated copper sulfate, the prothallia, while 
germinating much later and growing more slowly, broadened in the 
usual way. 
In the ordinary cultures, by the end of ten or twelve days an apical 
cell is established and a thallus is produced, first spatulate and then, 
by the more rapid growth of the cells on either side of the apical cell, 
