58 SEAWEEDS 
creeping dorsi-ventral thallus wholly unlike the 
upright Cutleria form. The hairs of the sterile 
portions of the thallus of the Cutleriacee 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 Cuéleria 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 
vogonia 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 
