606 LECTURE XXII. 



Amongst the Confervoideae, which are somewhat more 

 highly organised than the protophytic Algae, we find forms, of 

 which Ulothrix may be taken as an example, which likewise 

 produce macro- and microzoospores. The macrozoospores 

 simply come to rest and germinate. The microzoospores 

 may also behave in this way; but, as Dodel-Port observed, 

 they not infrequently coalesce in pairs, producing by their 

 coalescence a single cell of the nature of a spore which 

 on germination gives rise to a new Ulothrix-filament. 



Fig. 65 (after Dodel-Port). A conjugating microzoospores of Ulothrix. 

 B macrozoospore of Ulothrix. 



Comparing Ulothrix with Haematococcus, we see that in 

 both plants the macrozoospores are asexual reproductive 

 cells, that is, spores. This is true also of the microzoospores 

 of Haematococcus, but only to a limited extent of the micro- 

 zoospores of Ulothrix, for, instead of each germinating in- 

 dependently, they may coalesce in pairs, that is, go through a 

 sexual process. The microzoospores of Ulothrix are repro- 

 ductive cells which are intermediate between the altogether 

 asexual microzoospores of plants like Hsematococcus on the 

 one hand, and the altogether sexual reproductive cells of the 

 higher plants. 



The coalescence in pairs of the microzoospores of Ulothrix 

 is an instance of one of the simplest modes of the sexual 



