38 
F. 0. BOWER. 
0 
Fucus serratus. 
I chose F. serratus as the species best fitted for following 
the stages of development of the conceptacle for these reasons. 
(1) The fertile branches (Bliithen of Reinke) are less swollen 
than in other species^ and it is therefore easier to obtain 
sections through the apex ; while the tissues are more com- 
pact. (2) The hairs, which in later stages fill the cavity 
of the conceptacle, are not developed so early here as in 
other species. (3) F, serratus presents conceptacles of all 
ages in the month of August, at which time only I have had 
the opportunity of making collections. 
The first traces of the conceptacle are best observed in 
vertical longitudinal sections. 
In £he fertile branches of F. serratus I have noticed no 
deviation from the form of the apical cells, and the succession 
of their segments, described by Rostafinski (loc. cit.) for the 
sterile branches of F, vesciculosus. The division of the lateral 
segments cut off from the apical cells also appears to follow 
the type of his fig. 14, each segment dividing first by a wall 
parallel to its free surface Basalwand ; the outer of the 
two cells thus formed again divides in two planes at right 
angles to one another and to the Basalwand.” Four cells 
are thus formed, each of which may again divide according 
to the same law as the original segment ; this is the constant 
law of division of the cells of the normal limiting tissue of 
the younger branches, be they sterile or fertile (cf. fig. 1, 
groups marked 1). 
It is, however, in a modification of this succession of 
divisions that the first traces of the conceptacle make their 
appearance. Just as noticed by Rostafinsky (loc. cit., p. 9) 
for older branches, the division of the outer cell by vertical 
walls into four ceases in certain cases. The division by 
walls parallel to the surface (Basalwande) , however, continues. 
A linear series of cells is thus formed which may be traced 
some distance into the tissues, but which is terminated by a 
single cell only (fig. 1). Later, the activity of division in 
the horizontal direction also ceases, and as the terminal cell 
of the series does not increase in size, the result is that it is 
surpassed by the tissues surrounding it. 
The terminal cell of this series we may call the initial 
cell of the conceptacle, the cell immediately beneath it may 
be termed the basal ” cell. 
As the cells which abut laterally on the initial cell retain 
^ Thereby conveying no functional connection with an a))ical cell. 
