58 SEAWEEDS 



creeping dorsi- ventral thallus wholly unlike the 

 upright Cutleria form. The hairs of the sterile 

 portions of the thallus of the Cutleriacece grow by 

 transverse divisions of any of the cells and contain 

 chromatophores, while the root-hairs divide only at 

 their apical cells. 



The Reproductive Organs. These originate from 

 single epidermal cells and occur in Cutleria on both 

 sides of the thallus, and in Zanardinia on the upper 

 surface only. The oogonia and antheridia are borne 

 laterally on tufts or sori of hairs originating as de- 

 scribed, and consist of densely compacted tiers of 

 superimposed cells (four cells to a tier in the oogonia 

 and two in the antheridia), those producing the 

 oogonia being considerably larger than the others. 

 Each cell opens by a lateral hole, and in the 

 case of the oogonia produces one oosphere, of the 

 antheridia two antherozoids. Both kinds are bi- 

 ciliated, the oospheres much larger than the 

 antherozoids, and it is not until the former have 

 come to rest that impregnation is effected. Experi- 

 ments in effecting hybridity between Cutleria 

 multifida and C. adspersa were wholly negative, the 

 antherozoids being unattracted by the oospheres; 

 while observations of fertilisation within the species 

 have determined a definite attraction by the resting 

 oosphere towards antherozoids for some distance 

 around it. Parthenogenesis is said to occur. 



The non-sexual zoospores of Zanardinia are pro- 

 duced in unilocular sporangia, elongated and slightly 

 clavate as a rule, standing in dense rows side by side 

 and opening at the apex. Four to six zoospores are 



