206 Woodworth . — The Apical Cell of Fucus . 
other similar cells, and then a series of long cells. For a 
certain distance these diminish until they become of about a 
constant size, and are continuous with the epidermal cells, 
which dip down into the depression and together with all the 
cells above mentioned line the cleft, radiating as it were from 
the large triangular cell first spoken of. 
At the bases of the large central cell and the other lateral 
cells are many smaller ones, somewhat irregular in shape, 
forming a compact mass. Lower down they are more loosely 
arranged, and form filaments which are the upper ends of 
the hyphae composing the central tissue of the stem. A 
number of sections parallel to this present much the same 
appearance, the triangular cell perhaps becoming a little 
smaller. 
If a section be now made at right angles to the last, that is 
a longitudinal section in the direction of the elongated 
terminal depressions, and parallel to the broad surface of the 
frond, Fig. 2 will represent what is seen. In such a section 
the outline of the cavity will not have the steep sides, as in 
the first, but will be as a shallow depression. At the deepest 
part of the hollow is seen a cell (A) with convex sides and 
larger than any of the surrounding cells. This cell is quadri- 
lateral, the longer axis being up and down. The general 
shape is oblong, the base being somewhat broader than the 
upper or free end. It does not differ greatly in size from the 
cells on either side of it, and its most prominent feature is the 
convexity of both the sides, while the lateral cells are convex 
on one side only, that being the side farthest from the central 
cell. The lateral cells here also form a series on either side of 
the central cell, growing smaller as they become more distant, 
and eventually merge into the epidermis. Here again, as in 
the last section, there is seen a compact mass of small cells 
about the bases of the larger ones, running into the medullary 
hyphae of the stem. 
The central cell A in Fig. 2 is the central A in Fig. 1. 
The relations to the cells surrounding it are the same, the 
differences of appearances in form being due to the difference 
