Phylogeny 21 



types, but the fact must not be overlooked that these lowly types, 

 although they may have undergone many modifications, still 

 persist, and great care should be taken not to confound them with 

 those stages in the life-histories of the higher types which present 

 so many resemblances to them. 



THE PHYLOGENY AND CLASSIFICATION OF THE 

 FRESHWATER ALG.E. 



The researches and discoveries of the last few years have 

 certainly thrown much light on the affinities of many genera and 

 families of Alga 1 , and constitute a very great advance in our 

 knowledge of the phylogenetic relationships of these plants. It is 

 by no means an easy task to give even a mere outline of the 

 suggestions which have at different times been put forward as to 

 the evolution of freshwater Alga?, but one derives great assistance 

 from two recently published papers, one by Chodat 1 and the other 

 by Blackman 2 , containing not only a summary of much of the. work 

 bearing on this difficult problem of phylogeny, but putting forward 

 some well-founded suggestions as to the same. 



In the succeeding brief account of the evolution of freshwater 

 Alga? I have followed very largely the suggestions of Borzi, 

 Blackman, Bohlin and others, with certain alterations based upon 

 my own experience 3 . 



Taking first the Chlorophycea? or green Alga?, which a few 

 years ago were in a chaotic condition, we find that this chaos has 

 been greatly reduced to order and that the affinities of many of 

 these plants have been clearly demonstrated. The four groups 

 of the Confervoidese, Conjugate, Siphonea? and Protococcoideae, into 

 which the green Alga? have been usually classified, must be con- 

 siderably modified in view of recent researches. The Conjugate 

 and the Siphonea? will remain as distinct and natural orders of the 

 green Alga?, the former chiefly by reason of their reproduction and 

 the latter on account of their ccenocytic structure, but the Con- 

 fervoidea? and ProtococcoideaB were unquestionably unnatural 



1 Chodat, 'On the Polymorphism of Green Algae and the Principles of their 

 Evolution,' Ann. Bot. xi, 1897. 



2 F. F. Blackman, 'The Primitive Algre and the Flagellata. An Account of 

 Modern Work bearing on the Evolution of the Algas,' Ann. Bot. xiv, I'.tno. 



3 In 'Lectures on the Evolution of Plants' by D. H. Campbell (Macmillan 

 Company, New York, 1889), there is a chapter on Algae (pp. 4879) with a scheme 

 of evolution (p. 79), but the latter appears to be largely based upon erroneous 

 conceptions of the relationships of these plants. 



