402 BOTANICAL GAZETTE [NOVEMBER 
addition of darkly staining bodies; there is no trace left of nuclear 
structure. 
As active growth continues on each side of the initial row, 
rapid division occurs in the external layers of the thallus, whereas 
the inner cells, lying on the border of the central cavity, are pulled 
apart, not dividing to keep pace with the active outer tissue. 
This separation leaves the filiform basal process swinging loose, as 
it were, in the central cavity (figs. 17-20). The entire structure 
lies at the base of a slight depression, the result of arrested growth 
of the initial row followed by activity of abutting tissue. 
Such, then, is the history of the initial row. Jt is the result of 
more or less disintegration of an entire linear row of the thallus, with 
perhaps the addition of portions of a terminal hair. The exact 
amount of tissue originally involved, whether including a terminal 
hair in part or in entirety, determines the length and size of the 
mature structure. For a long time the writer was puzzled by the 
great variation in length displayed by these bodies, and the explana- 
tion was apparent only when their origin was completely worked 
out. 
The structure described in the foregoing is found in connection 
with any activity of the plant, as growth at the main apex, or 
production of lateral branches, or inception of conceptacles. 
The conceptacle 
In the formation of the conceptacle, the cavity in which the 
initial row lies becomes deepened as more and more of the abutting 
border tissue is involved. Rapid radial division of these border cells 
contributes new tissue to the conceptacle at the same rate and in the same 
way as ordinary thallus tissue is developed. In the early stages 
of the conceptacle, except for the initial row, there is no essential 
difference between adjacent tissue of the thallus and that of the 
actual cavity of the conceptacle (fig. 19). Presently, however, the 
lining cells of the conceptacle become elongated, and subsequently, 
by transverse division at the basal end, develop into septate hairs 
(figs. 20, 21). This behavior is exactly as noted by the writer in a 
recent investigation of Fucus (14) as the stage in the history of the 
conceptacle known as the “hair pit.” 
