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 

 the thallus-cell itself, as 



FIG. 78. a, Ceramium diapha- ,, L i\ s-\ xi r 



ntim with nodal cells ; ft, procarp USUaliy Stated). Un the ier- 

 of Callithamnion gracillimnm .,. . ~ , 



highly magnified. (5, after tlllSatlOn of the CarpOgOU- 

 Schmitz.) . ,-, -i i n / 



mm, 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 



