59 



emitted by each sporangium. While the thallus 

 that bears these sporangia in Zanardinia is of the 

 same structure as that which bears the antheridia 

 and oogonia, it is otherwise, as has been said, in 

 Cutleria. The young plants produced by the germ- 

 inating zygote of Cutleria are wholly different from 

 the upright thallus of the sexual generation, and 

 these young plants have always proved sterile so far 

 as cultivated specimens directly observed are con- 

 cerned ; but they apparently agree so well with the 

 plants formerly known as species of Aglaozonia 

 which do bear zoosporangia like those of Zanardinia, 

 that it may be fairly concluded there is an alternation 

 of generations between the sexual Cutleria plants 

 which never bear zoosporangia and the non-sexual 

 Aglaozonia plants. 



There is a resemblance between the sori of anther- 

 idia and oogonia in Cutleriacece and the sori of similar 

 organs in Fucacece, situated though these are in con- 

 ceptacles. Sometimes the oogonia of the Cutleriacece 

 are terminal on unbranched hairs, while the 

 antheridia are, at least those in the middle of the 

 sori, more copiously branched. The oogonia on 

 branching hairs in Sarcophycus may be recalled 

 for comparison, while the paraphyses in both 

 orders are not unlike in many respects. The 

 Cutleriacece are unique, however, so far as is known, 

 in the possession of ciliated oospheres of greater 

 size than the antherozoids (cf. Codiacece), but other- 

 wise resembling them, and this cardinal fact points 

 to relationship on the other hand with the orders of 

 Phceophycece in which the gametes are both motile, 



