252 



THE ALGAE 



Rkodomelaceae '.Janczewskia (after E. de Janczewski). Fig. 142 



This is a remarkable hemi- or holo-parasitic genus which is 

 always to be found on other members {Laurencia, Chondria and 

 Cladhymenia) of the same family. One of the most interesting 

 features of this parasitism is that the genus is very closely related 

 to Laurencia and yet is parasitic upon various species of that genus. 

 All the species have organs of contact or penetration, the latter 

 being fungal-like filaments which estabUsh pit connexions with the 

 cells of the host. Each individual plant is a whitish, coalescent 

 tubercular mass composed of fused branches that grow from an 

 apical cell buried in a pit as in Laurencia. The sexual plants are 

 dioecious and the diploid asexual plant also occurs. 



Fig. 143 a, Laurencia papulosa, part of plant ( x li); b, t.s. axis of 



L. implicata. The central axis and four primary siphons are clearly 



visible ( x 60). (After Borgesen.) 



