94 SCIENCE PROGRESS 



fervales is a very uncertain one and opinion is again veering 

 round to the view of the Siphoneous affinities of this genus 

 (Oltmanns 53 and 54, Lotsy 46; cf. also Wille 70a). There is no 

 doubt a good deal to be said in favour of such an affinity, and we 

 may briefly review such evidence as is available. The peculiar 

 multiciliate zoospore (so-called synzoospore) of Vaucheria no 

 doubt represents the entire contents of a zoosporangium which 

 have failed to become separated from one another (Schmitz 60). 

 This is shown by the fact that the cilia arise in pairs opposite 

 the numerous nuclei and that the vacuole of the zoosporangium 

 remains included within the body of the massive zoospore, 

 although, as a rule {e.g. in Codium, Ulotlirix, etc.), the vacuole 

 of the zoosporangium is not employed in the formation of the 

 zoospores. This compound zoospore is therefore quite homo- 

 logous with the gonidium of a Fungus like Pythhim (except that 

 the latter remains enveloped by the wall of the sporangium) or 

 other of the Peronosporaceae, and may be regarded as a peculiar 

 expression of tendency in Vaucheria^ to be sought for in the 

 allies of the latter. The work of various American botanists 

 (Davis 19, Stevens 65, and others) on the cytology of the sexual 

 organs of the lower Fungi (Phycomycetes) has shown that these 

 organs, even when outwardly oogamous ^ in character, are to 

 be regarded as derived from gametangia, in which the gametes 

 do not become distinct from one another (constituting a so- 

 called coenogamete). In many of these forms the ccenogamete 

 has become uninucleate by diverse methods of suppression of 

 the remaining nuclei, all of which are functional, for instance, 

 in such a form as Cystopus Bliti (Stevens 65). On the basis of 

 this and other pieces of evidence the view that the Phycomycetes 

 have arisen from a siphoneous algal ancestor has become fairly 

 well established ; in this connection we may call to mind 

 the fact that there is a marked saprophytic and parasitic tendency 

 among the Protococcaceous allies of the Siphoneae (cf. the first 

 part of this article, p. 645). In the oogonium of Vaucheria we 

 have a structure which is a multinucleate coenogamete to begin 

 with, although it subsequently (as in many of the Phycomycetes) 

 becomes uninucleate in a way about which there is still some 

 difference of opinion (Oltmanns 52 and 53, Davis 20, Heidinger 

 32). Nevertheless, both in its oogonium and its zoospore Vaii- 



' The pseudo-oogamy may perhaps be an arrangement for the better nourish- 

 ment of the female cell. 



