409 
Rhahdonict tenera , J . Ag> 
a mechanical system with the mechanical elements arranged 
in a ring around the conducting system. The numerous 
types into which he has sought to separate the Florideae 
on anatomical-physiological grounds have so little value, 
that I have not considered it necessary to refer Rhabdonia 
to any one of them. In his work on the storage-system of 
Florideae (Wille, ’87), Rhabdonia is not mentioned. 
The structure in the region of the holdfast corresponds in 
general to that described above, but the intercellular spaces 
are almost entirely lacking, and the closely packed cells, 
which are arranged so as to give the greatest mechanical 
strength, are square or angular in section. Just above the 
holdfast the distinction between medulla and cortex entirely 
disappears. All the cells of the holdfast and the region 
directly above it are densely filled with Floridean starch. 
It is not impossible that in winter the plant may die down 
to the holdfast, which may in the spring regenerate the lost 
portions. 
The cortical cells near the tip of the frond often bear long 
unicellular hairs, which soon drop off and leave the surface 
of the frond perfectly smooth. 
The cells are connected by primary pits which arise at 
division, and by secondary ones which are formed subse- 
quently. Shortly after the formation of a pit, the cell-wall 
immediately around it becomes swollen and highly refractive ; 
and, as the cell grows older, forms a fairly thick, highly refrac- 
tive circular plate (Fig. io at the left). In the oldest cells 
it often happens that such plates become separated into two, 
which are connected by a delicate strand of apparently proto- 
plasmic substance (Fig. i, between st and cpg). 
If the connecting substance is really protoplasm, it is 
without doubt continuous through the plates with the proto- 
plasm of the cells lying on either side. According to Wille 
(’85) such plates in Cystoclonium purpurascens and some other 
Florideae are pierced by numerous pores like the callus-plates 
of Laminariaceae. 
Both kinds of spores are uninucleate. The younger 
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