RHODOPHYCE, OR FLORIDEA 201 
individual cells, not by their transverse division, or 
by their median longitudinal division. Portions of 
the margins of the individual joint-cells may how- 
ever be cut off by dividing walls, and these then 
develop into lateral branches. As this process may 
happen but once, or many times, simultaneously or 
in succession, varied modes of branching of the cell- 
filaments are produced. 
Each cell of the filament is provided with a central 
pit in the cross-wall, and since such pits do not occur 
in the marginally cut-off cells, their presence or 
absence enables us to trace ina tissue the genetic 
connection of the individual cells with their neigh- 
bours. However, this frequently becomes complicated 
by the occurrence of secondary pits, formed subse- 
quently between individual cells of the thallus. The 
pits are not open pores, permitting free passage of 
cell-contents such as nuclei and chromatophores, but 
they are closed by an exceedingly thin membrane. 
On both sides of this closing membrane there is a 
comparatively thick plate of a dense substance, 
recalling in its characteristics the mucilage-masses 
of the sieve-tubes of the higher plants. These plates 
adhere firmly to the closnmg membrane on both its 
sides, one in each cell, and they are connected with 
each other by numerous cords which perforate the 
closing membrane, mostly round the margin of the 
pit. The plates stand in direct connection with the 
protoplasm lining the cell-wall and are, in fact, so 
coherent with it, that they may be regarded as 
transformed or rather differentiated protoplasm locally 
covering the pit. However, it is probable that a thin 
