sus ul 
ne 
Fig. 423. 
Odonthalia dentata. A, transverse section of frond from 
the last year. B, longitudinal section of cells of the inner 
tissue (pericentral cells or inner cortical cells), connected 
by three secondary pits. 150:1. 
460 
shorter and are connected with each 
other by one to three, mostly secondary 
pits in the transversal walls (fig. 423 B). 
They contain several nuclei and produce 
many starch grains when the growing 
period has ceased. The cells surrounding 
the central cell are longer and constitute 
together with it a conducting system (comp. 
Wille 1. c.). The older, at least one year 
old parts of the frond are provided with 
a more distinet mid-rib projecting on both 
faces of the frond. Its appearance may be 
somewhat irregular, the rib being present 
on a certain stretch, disappearing further 
downwards and then reappearing definitely, 
and the two ribs are not always exactly 
opposite to each other. This rib is composed of cell-rows directed outwards and 
then in a bow obliquely downwards and united into a compact tissue, the surface 
of which is even. Wırre’s fig. 48 (1885) evidently represents a transverse section of 
such a mid-rib. He regards this tissue as belonging to the assimilating system; it 
has in my opinion rather 
a mechanical function. 
The germination has 
not been observed, but 
young plants, about 3 mm 
high, were found in the 
northern part ofthe Sound 
off Aalsgaarde, on a shell 
of Cyprina islandica in a 
depth of 19 meters (fig. 
424). The smallest one (A) 
which did not reach 2 mm 
in length was entirely un- 
branched. It had a terete 
stipe continuing in a nar- 
row lanceolate lamina, the 
upper part of which is 
shown in fig. D. Numerous 
marginal initial cells sim- 
ilar to those shown in fig. 
422 B are to be found in 
Odonthalia dentata. 
Fig. 494. 
A—C, plantlets found growing on Cyprina islandica, B 
and C, with an adventitious hranch. D, upper end of À more highly mag- 
the edge. A couple of some- 
nified. E, young adventitious branch. 
4A 50:1. B,€ 18:1. D, E 30:1. 
