264 
layers of cells, not including the cortical cells, and further transversal divisions fre- 
quently do not occur except in the immediate vicinity of the conceptacles; it may 
even happen that the frond is monostromatic in almost its whole extent. The long 
cells in the upper layers are always connected with transversal pits (fig. 184). 
The thickness of the frond is rather variable. Monostromatic fronds were 25—42y 
thick, fronds consisting of two layers of cells 67—105 and fronds containing three 
layers were 91—123, thick. The fronds are frequently growing over each other. 
It also frequently happens that new growing edges are produced from certain parts 
of the frond, growing over the neighbouring parts the growth of which has ceased. 
The long cells contain a small nucleus in the upper part of the cell, and a number 
of small chromatophores spread in 
the cell. The cortical cells are pro- 
duced early, immediately after the for- 
mation of the long cells by the divi- 
sion of the marginal] cell. But at some 
distance from the margin a new cor- 
tical cell may be cut off under the 
primary one by a horizontal or in- 
clined wall (fig. 184 B), and this pro- 
cess may be repeated several times. 
Hyaline hairs may be produced from 
long cells seemingly not different from 
Fig. 184. the others, and provided, like these, 
Lithophyllum macrocarpum f. intermedia. Vertical sections of with a cortical cell (fig. 184 B). The 
fronds. A, margin of frond. B, part of monostromatic frond 
showing a hair-cell and two cortical cells cut off from one cell. length of the long cells of the frond 
G, part of thicker crust: transversal pits” between the cells varies greatly; when the crust is po- 
of the two upper layers. 350:1 eg 
lystromatic, the cells of the under- 
most layer are often rather short. When these cells or those of the monostromatic 
frond are long, their undermost part is usually more inclined than their upper part 
(fig. 184 B, comp. NıcHors, L. c. fig. 12, 15). 
The sporangial conceptacles are very prominent, conical with rounded or ap- 
planated top, 300—500 z in diameter. Under the conceptacle 1—3 layers of sterile 
cells are present. Papille projecting inward and upward, lining the pore, as de- 
scribed and figured by NıcHoLs, may be found in the under part of the pore, but 
they are usually slightly developed. Seen from above, the superficial cells sur- 
rounding the pore appear scarcely different from the others, the nearest being only 
a little smaller (fig. 185 B). The sporangia are only placed in the peripheral part 
of the conceptacle, the central part being occupied by sterile cells forming a conical 
columella. NıcHors found also sporangia in the central part, though less numerous 
there than at the periphery. As shown by this author, each sporangium is born 
by a stalk cell. A “plug” was found in some rare cases in the ostiole, forming a 
continuation of the central sterile cells (fig. 185 A), but it seems to be usually wanting, 
u 
