Rhabdonia tenero , J. Ag. 417 
exclusively from the sterile cells of the branch containing the 
auxiliary cell. 
Development of the Carpostome. 
The development of the carpostome begins quite early, and 
by the time conjugation with the auxiliary cell has taken 
place a considerable depression has been formed in the 
exterior of the frond just over the auxiliary cell (Fig. 3). It 
arises as follows : some of the filaments proceeding from one 
of the two lateral cells borne by the auxiliary cell cease to 
grow, and finally the terminal cells (i. e. the outermost) perish 
(Figs. 2, 3, 4, 5 and 1). These cells are easily recognized in 
preparations of living material by their greenish colour. The 
cells of the filament then die as far back as the large cell 
which is borne on the auxiliary cell, and an opening is thus 
made to the exterior. In the meantime the filaments in the 
immediate neighbourhood have commenced the rapid growth 
already mentioned, and those nearest the carpostome produce 
around it a lining of very small cells (Fig. 1). A surface view 
of the carpostome shows the cortical cells of the pericarp 
arranged in rows, which radiate from the carpostome in all 
directions. 
Theoretical Considerations. 
Whether the cystocarp of the Florideae represents a sporo- 
phyte or not, must remain for the present an open question. 
The fact that we are not able to sa y whether the trichophore 
or the auxiliary cell, or both, are fertilized does not affect the 
question, so long as the sexuality itself is not called in 
question. The grounds on which the sexuality of the 
Florideae has been questioned, are the result of erroneous or 
incomplete observation. The statements of Bornet and 
Thuret to the effect that the cystocarp often originates from 
cells which are separated from the trichophore and which do 
not fuse with it, were made under the impression that fusion 
was not necessary to ensure fertilization. They consequently 
