236 SEAWEEDS 
crown of cells covering the place where the parent 
cell is joined with the one above it. In some cases 
these filaments completely clothe the main cell row, 
in others they fail to meet and leave intervening 
parts bare. The procarpia are therefore external, 
and the gonimoblast is usually destitute of any 
envelope, but such does occur. The gonimoblast (of 
which there are usually two in each cystocarp) forms 
successively several lobes, of which nearly all the 
cells give rise to spores. Callithamnion, one of the 
commonest genera, may be taken as typical of the 
others in the matter of its reproduction. From 
one of the joint cells of the 
thallus there issue (besides 
the vegetative lateral shoot 
from its upper end) two small 
unicellular outgrowths from 
about the middle of the cell. 
From one of these a three 
or four-celled carpogonial 
_ branch proceeds (not from 
sek Bc areas ance: the thallus-cell itself, as 
num with nodal cells ; b, procarp usually stated). On the fer- 
of  Callithamnion gracillimum , -,- : 
highly magnified. “(%, after tilisation of the carpogon- 
Schmitz.) - 
ium, the basal cells (or more 
rarely. one of them) of the two original lateral 
outgrowths segment off each a daughter-cell, and 
these become the auxiliary cells. The fertilised 
carpogonium then extends a little sideways towards 
the auxiliary cells, and it also segments off its pro- 
truding parts as separate cells. These then conjugate 
with the auxiliary cells by means of an exceedingly 
