972 
show particular apical cells nor a marginal series of apical cells but consists of a 
great number of close cells without distinct arrangement. The frond is built up 
Fig. 567. 
Rhodymenia palmata. From Eastern Kattegat, near Læsø Trindel, 19 m. May. Photo, ?/, nat. size. 
of an inner tissue of one or two layers of large thick-walled cells, a medullary 
layer or mechanical tissue (WILLE 1891, p. 104), and an outer assimilating tissue 
Fig. 568. 
Rhodymenia palmata. 
Superficial cells from 
young plant. 622 : 1. 
consisting of 1 to 2 layers of smaller cells containing numerous 
chromatophores (fig. 568). An intermediate layer, (secondary 
mechanical tissue WILLE), is situated between the assimilating 
and the medullary layers. 
The young fronds and frond-segments bear numerous 
hyaline hairs, developed from ordinary peripherical cortical cells 
from which they are separated by a basal wall situated at the 
level of the surface of the frond (fig. 569). The hairs appear on 
the young plants, but only when they have reached a length of 
about 8 mm. In the older fronds the hairs only occur in the young segments while 
they are still growing. The hairs are very numerous but are confined to distinct 
