558 
tissue thus serves to convey the products of the assi- 
milation to the central cylinder, and later to transport 
the dissolved nutrient media from the central tissue to 
the periphery. 
The cortex has about the same structure as the 
basal disc; it is composed of small, nearly squarish 
cells with slightly rounded angles, arranged in radial 
rows having the same diameter in their whole length 
(comp. KüTziNG, 1869, pl. 66, fig. e, WILLE, 1885, 
fig. 11). The cell-walls are moderately thick, the outer 
wall thicker, firm, not gelatinous. The whole cortex 
has a firm structure owing to the small diameter of 
the cells, and certainly contributes to the rigidity of 
the frond. The cortical cells contain one small nucleus. 
The chromatophores are not easy to distinguish owing 
to the small dimensions of the cortical cells. There 
often seemed to be one parietal plate at the upper 
end of the cells; but in a specimen treated with FLEN- 
MING’s weaker solution and stained after HEIDENHAIN 
with erythrosin and examined under high power several 
disc-shaped chromatophores 
Fig. 547. were observed in each cell, 
eg mes SIMONI hn 1S, BAS) 18), GEIR 
also the primary pits are to 
be seen. Secondary fusions between cells of different cel — 
rows now and then appear (fig. 548 A). The cortex 
of the older fronds shows a stratification which is the LUE 
effect of a periodical increase in thickness, which has Bron 
been the subject of a thorough investigation of B. JOns- 0 
SON (1891). The growth in thickness takes place in toit 
the outermost layer of cells which keep their dividing * \ 
power. This, however, is not always in activity but is DOGS 
interrupted by resting periods leaving their trace in Øg C 
boundary lines characterized by thicker and more re- Fig. 548. 
fractive membranes. Jonsson thinks these boundary lines  {nnfeltia plicata. Transverse sec- 
arise because the walls of the outermost celis become thicker nn ena 
and more refractive than the inner walls during the resting showing pit-connections and chro- 
period, whereas the new cells formed at the beginning Re are EN Sam 
of the growing period have comparatively thin walls. This layers (*) 1200 : 1. 
explanation is certainly true but the figure (l.c. plate I, fig. 4) 
illustrating it does not give a true idea of the real structure. The boundary line is shown 
by Jønsson as a continuous thick wall corresponding to the outer wall of the frond, 
