156 
or exogenous and, according to this author, the cells of the short-celled filaments 
are divided by intercalary divisions. 
The structure of the frond has been described in 1847 by NÆGELI (l. c.). It 
terminates in an apical cell which is said to be divided by oblique cell-walls pro- 
ducing segments at all sides, and this is affirmed by Scumirz and HAUPTFLEISCH 
(ENGLER u. PRANTL, Nat. Pflfam. I, 2 p. 517); it is however at least not general. The 
young fronds arising from the basal disc have at all events an apical cell divided 
by horizontal parallel walls, and this is also the case with young slender branches 
(fig. 74, B, C). In thicker shoots still in development I have found the segment walls 
somewhat inclined, but not 
so much that they reached 
the foregoing segment wall 
(fig. 24, C). The cells of the 
frond contain a single nu- 
cleus and a number of disc- 
shaped chromatophores. 
Some of the surface- 
cells may produce a hya- 
line hair of the same cha- 
racter as in other Florideæ 
(fig. 74, D). In spring (March 
to May) they are most devel- 
oped, numerous, long and 
rich in protoplasm; at 
other seasons they are often 
wanting. 
Fig. 74. 
Dumontia incrassata. A, five days old plant from germinating tetraspore. à 2 
B, upper end of side branch showing transverse segment walls. C, tip of vanced age it becomes ir- 
cylindrical, but in an ad- 
A etn pees au 
F, transverse section of frond showing the development of the antheridia. crisped (£. crispata Grev.). 
A 300:1. B,C, E 390:1. D, F 630:1. In agiater an in Badel 
localities it is dark red-brown, while in sunny places in spring and summer it has 
a light yellowish colour, the tips at last becoming green. 
The central cavity contains a thin ‘slimy matter which seems to consist of 
pectic substances; it forms a network in the cavity, the meshes containing probably 
only water. 
The sporangia are, as is well known, immersed in the wall of the frond; they 
are born of a cell in the inner cortex bearing moreover at least two cortical fila- 
ments (comp. Kirzine Phye. gen. tab. 74 II). The sporangium is connected through 
a pit with the bearing cell but not with other of the cortical cells (fig. 74, E); thus 
it is terminal and not intercalary as in Dilsea. The division is always cruciate; but 
The frond is at first 
