THE GREEN ALGiE 93 



plast (cf. Hydrodictyon). The acquisition of the multinucleate 

 condition led to a gradual loss of the power of forming separating 

 walls ; and so, according to Oltmanns' theory, we would get 

 by successive stages the Valoniaceae, the Dasycladaceae and the 

 typical Siphoneae. It is impossible with the limited space at 

 my disposal to deal with all the evidence in favour of this view 

 but it may be mentioned that the thick annular ingrowths 

 (resembling arrested transverse septa of a Cladophord) occurring 

 at perfectly regular intervals in the threads of diverse members 

 of the Codiacese (Ernst 24, Kuster 43) are interpreted as 

 remnants of original septa, whilst the formation of separating 

 walls in connection with the gametangia of many of the 

 Siphoneae is looked upon as a reminiscence of an ancestral 

 feature. Oltmann's theory, therefore, involves our giving up 

 the view of the Protococcaceous origin of the Siphonales, and, 

 as a matter of fact, completely inverts this series, the Clado- 

 phoraceae becoming the simplest forms and Caulcrpa, Bryopsis, 

 etc., the most highly developed. In view of the very obvious 

 siphoneous tendency of the Protococcaceae this seems a rather 

 forced position and one's sympathies will naturally incline to 

 the older theory, which places the Siphoneae first and derives 

 the Siphonocladeae from them. There may, however, be some 

 doubt whether the typical Cladophoraceae {CladopJiora, RJiizo- 

 cloniiim, ChaionwrpJia, etc.) really belong to the Siphonocladeae 

 at all, and whether just these representatives are not phylo- 

 genetically connected with the Ulotrichales. To me there seems 

 much to favour this view, although I should derive all the 

 remaining Siphoneae from a Protococcaceous ancestry by way 

 of some simple form like Protosiphon. 



Before leaving the Siphonales it is necessary to consider 

 briefly the position of the genus Vaucheria. In recent years 

 there has been a tendency to remove this genus from among 

 the Siphoneae, chiefly on account of its peculiar zoospore (fig. 

 3, k), its method of sexual reproduction, and the formation of oil 

 as an assimilatory product (Bohlin 9, Blackman and Tansley 6). 

 For the latter reason and owing to the fact that the two cilia 

 of the spermatozoids point one forwards and one backwards, a 

 position among the Confervales (Heterokontae) has been advo- 

 cated (see below, p. 104); the frequent yellow-green colour of the 

 chloroplasts has also been brought forward in support of this 

 view. Nevertheless, the position of Vaucheria among the Con- 



