134 Grubb .— The Attachments of Porphyra umbiticalis. 
a further portion of the chromatophore passes down, and this is seen causing 
a bulge in the wall in its journey towards the tip (Text-fig. 2, b). 
The full-grown filament, before modifications have taken place, consists 
of a very long, exceedingly narrow refractive tube, with thick gelatinous 
walls and no cross-walls. A typical filament with its disc cell attached, 
which was separated out and measured, was found to be over n mm. in 
length ; in discs of Ulva with a similar structure Thuret ( 9 ) states that the 
filaments may reach io mm. (cp. 4 ). The staining contents consist ^ of 
numerous fragments of chromatophore and many highly refractive minute 
Text-fig. i. Longitudinal section through the 
attaching base of Porphyra umbilicalis , showing the 
central rows of cells (c) and the interwoven branching 
filaments. At A the proliferating portion is seen, and 
at B this portion is occupied by a colony of blue- 
green algae. Drawn with camera lucida. x 150. 
Text-fig. 2. Outline drawings of 
the cells and filaments composing the disc 
of Porphyra. At a the first stage in the 
formation of the young filament is seen, 
showing the chromatophore and nucleus 
in the tip. b shows a second portion of 
chromatophore passing down, c, a disc 
cell producing two filaments. D, a disc 
cell with a cross-wall. Camera lucida 
drawings, x 750. 
nuclei which are scattered along the length of the tube (PI. I, Fig. 1). As 
a rule only one filament is formed from a single cell, though occasionally 
two may be produced (Text-fig. 2, C) ; spores, on the other hand, have 
never been seen forming from a disc cell, and only in one case has the latter 
been seen with a cross-wall (Text- fig. 2 , D). 
The disc filaments pursue a winding course towards the base of the 
attachment, becoming interwoven with one another and forming a resistant 
tissue several layers in thickness. As they approach the substratum altera¬ 
tions take place in their structure, and the shorter threads, which are formed 
from cells with thick gelatinous walls in the centre of the tissue, appear to 
be twice the diameter of the normal filament. The tips of the majority of 
