22 



ALGA. 



, 



The oogones are divided into thirty-two or sixty-four cells, each of which 

 produces an oosphere. The oospheres are at first biciliated swarm-cells 

 or zoospheres endowed with active motion, closely resembling .the zoo- 

 spores of other Phasosporeae, but are -larger and variable in form one of 

 the very few instances known in the vegetable kingdom of the occurrence 



of such, organs. They are 

 said to be destitute of a 

 nucleus. The antherids are 

 also divided into a number 

 of cells, each of which pro- 

 duces two antherozoids, the 

 normal number in an an- 

 therid (in Cutleria adspersa, 

 De Not.) being 128. The 

 antherozoids are also bi- 

 ciliated swarm-cells, but 

 smaller than ttye oospheres ; 

 they have each an orange 

 pigment-spot, and are iden- 

 tical in structure with those 

 of the Fucaceae. The an- 

 therozoids do not approach 

 the oospheres until the latter 

 have come to rest and lost 

 their cilia ; the absorption 

 of a single antherozoid into 

 the oosphere is then suffi- 

 cient to impregnate it ; it 

 becomes invested with a 

 cell-wall of cellulose, and 

 begins to germinate at 

 once. Thuret states that 

 in C. multifida (Grev.) the 

 oospheres germinate with- 

 out having been fertilised. 

 The thallus resulting from 

 the germination of the im- 

 pregnated oospheres is said to be dorsiventral, producing rhizoids on 

 the ventral side only. Zanardinia produces also non-sexual zoospores 

 iri unilocular sporanges ; and has another non-sexual mode of pro- 

 pagation, by budding. In Aglaozonia .reptans (Ktz.) the non-sexual 

 zoospores are the only reproductive organ known ; and Falkenberg 





FIG. 226. Cutleria itniltifida. Grev. (natural size). 

 (After Hauck.) 



