554 Transactions. 
this type had a primary stipe measuring 90 cm., and one of the secondary 
stipes, with its lamina, measured А 
The stipe increases in thickness from year to year, the diameter in some 
of the larger specimens varying from 5 cm. to 7-5cm.; one exceptionally 
large one measured 12-5 em. Such thicknesses are exceptional for seaweeds, 
but in the case of Durvillea, as mentioned before, the stipe has partially 
to support its huge segmented lamina when it is left uncovered at low 
tides, hence its need of a stout tissue. The thickness of the stipe of Durvillea 
is exceeded by the big Laminarian Postelsia palmaeformis, whose huge stipe 
is strong enough to maintain an upright position in the air and support 
its tuft-like lamina (Campbell, 1902, p. 127). 
Three distinct tissues may always be recognized in the stipe, whether 
young or old: (1) an outer cortical assimilatory layer, (2) a filamentous 1 
conducting tissue, and (3) a central tissue. 
The surface layer of cells (figs. 5, 6, а) appears to be differentiated from 
the rest of the cortical tissue. The constituent cells are rather small, some- 
what cubical in shape, and at the same time more densely filled with cell- ig 
contents. Below this comes the rest of the cortical tissue (b), several cells 
in thickness, containing abundant protoplasm and rich in brown colouring- 
T ; 
matter. These cells are arranged in radial rows round the stipe. The inner- . 
most cells of this layer lose their characteristic oval form and show a ten- 
dency to branch and elongate. They pass gradually into the next tissue (c), — 
which is a mass of interwoven filaments. In longitudinal section (fig. 6 
these appear to lie close together, and run more or less in a longitudinal 
direction. In transverse section (fig. 5) they appear to be arranged in rows 
continuous with the rows of the outer layer. Towards the centre of the 
stipe this arrangement becomes less regular, and in figs. 5 and 6 (c) the 
longitudinal filaments are seen cut across. These filaments are interrup 
by other septate filaments running in a transverse direction, which serve to 
bind them together and make the tissue firmer. 
The central tissue (d) is composed of a mass of cells of varying shapes. 
There are few filaments to be seen both in transverse and longitudinal sec- 
tions, but the greater part of this tissue is made up of large cells, arranged 
À stipe with a diameter of 4 cm. was taken and cut into thin layers | T 
about 0-5 ет. thick. Some were placed in water, others in 30 per cent. x 
and left all night. In the 
m 
tissue had turned a bright green. When left longer in the alcohol dl 
show 
that the green colour was due to small round green bodies in the larger 
Joh kh 
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