46 
F. O. BOWER. 
a beaded series ; a basal part consisting of cells with only 
small quantity of protoplasm and slightly swollen cell-walls ; 
this lower part of the hair gives the impression of having 
shrunk similarly to the initial cell of the conceptacle of 
Fucus. Tracing this hair back it may be seen, when viewed 
from the surface, to pass into a cavity between the adjoining 
cells of the limiting tissue (fig. 10). This cavity is formed, 
as in Fucus, by the shrinking of the lower cells of the hair 
and swelling of the contiguous cell-walls, so as to fill the 
space thus formed. Fig. 11 shows a conceptacle of Himan- 
thalia at a slightly older stage in longitudinal section. The 
upper part of the hair has broken away, leaving only a single 
cell of the series behind. This cell is shrivelled and the 
cell-walls swollen, giving it the same appearance as the 
initial cell of Fucus, of which it is undoubtedly the equiva- 
lent. The form and size of this cell is very inconstant ; 
sometimes two such cells of the initial series are left behind. 
There is no cell in Himanthalia which may be easily 
recognised as corresponding to the basal cell of Fucus. This 
is probably owing to the distortion of tissues which often 
occurs at a little distance from the apical cell. 
During this change in the original hair, the cells of the 
limiting tissue, which immediately surround it, do not grow 
as rapidly as the adjacent tissue ^they only divide rarely in 
a direction parallel to the surface ; but more frequent and 
active division takes place in a direction perpendicular to it. 
The result is a depression of the surface around the initial 
cell. The tissue lining the cavity thus formed is therefore 
derived only from the limiting tissue ; no part of it is derived 
from the cortical tissue. The further development of the 
conceptacle is carried on chiefly by divisions according to 
the same rule as at first. The region of greatest activity 
is at the base of the cavity. Thus the conceptacle attains 
the form of a long tube, which widens later at the base, 
so as to assume the usual flask form. As this widening pro- 
ceeds, hairs are formed, as in Fucus, by outgrowth of single 
cells of the lining tissue. In a female conceptacle these 
hairs are multicellular but unbranched. In the male con- 
ceptacle the hairs are branched, at first on a monopodial 
system developed in a racemose manner ; i. e. the apical cell 
divides transversely, and the upper cell grows on as before ; 
the lower cell puts out a protuberance immediately below 
the dividing cell-wall. This does not, however, overtop the 
apical cell (cf. fig. 12). The apical cells of such hairs do not 
usually form antheridia; only the lower branches undergo 
the change. Coincident with the formation of the an the- 
