THE PHYLOGENY AND INTER- 

 RELATIONSHIPS OF THE GREEN ALG^ 



(Contiimed from p. 648 j 



By F. E. FRITSCH, D.Sc, Ph.D., F.L.S. 

 University of London, University and East London Colleges 



The first instalment of this article (Science Progress, No. 16, 

 April, 1910, pp. 623-48) was devoted to a discussion of the lower 

 unicellular and colonial representatives of the Green Algae. 

 We may now pass on to consider the higher filamentous types. 

 Among these we are in the first place concerned with the two 

 series of the Siphonales and Ulotrichales, both of which, as we 

 have seen, are probably derivable from the Protococcaceous 

 stock. The strictly siphoneous {i.e. non-septate) forms of the 

 Siphonales no doubt constitute a very natural group, about 

 the present-day classification of which there is practically no 

 difference of opinion (Wille 68, Blackman and Tansley 6). A 

 form like ProtosipJion (fig. 3, e, p. 644^) is mostly looked upon 

 as the starting-point ; from it evolution no doubt went on in 

 the various directions exemplified by Bryopsis and Caulerpa 

 on the one hand and the Codiacese and Dasycladaceae on the 

 other. Space does not admit of our dealing with these different 

 types but a brief consideration of Protosiphon will be useful 

 (Klebs 40). This is a small coenocytic organism inhabiting damp 

 mud and consisting of a green vesicular subaerial portion and 

 a long thin subterranean rhizoid, which is colourless. The 

 subaerial portion contains a reticulate chloroplast (cf. Hydro- 

 didyon), readily derivable, however, from that of the Chlamydo- 

 monad type by way of a form like Chlamydouionas reticulata 

 (Goroschankin 30), in which the chloroplast shows a tendency 

 to reticulation ; the reticulate chloroplast of Protosiphon some- 

 times breaks up into segments, and this probably indicates the 

 way in which the numerous small discoid chloroplasts of the 

 majority of the Siphoneae were evolved. Internal to the chloro- 

 plast of Protosiphon numerous small nuclei lie embedded in the 



' The page refers to the position of the figure in the first part of this article. 



91 



