92 MOORE— MOST PRIMITIVE LIVING REPRESENTATIVE [April 24, 



highly differentiated brown or red algae, but rather to the green algae, 

 in which group there exists the closest resemblances to the structure 

 of the lower land plants. The problem thus becomes one of discov- 

 ering as nearly as may be possible the most primitive member of the 

 green algae. And by "primitive/' of course, is not necessarily meant 

 the simplest form, but that plant which seems to be nearest to the 

 starting point of the phylogenetic tree and from which certain defi- 

 nite lines of ascent can be traced. 



In considering the origin of the green algae, numerous theories 

 have been held and it would be impossible to give even a mere 

 outline of the various improbable suggestions which have been 

 advanced regarding the evolution of this group. During the past 

 ten years, however, a great deal of light has been thrown upon the 

 phylogenetic relationship of the algae. Not only has the increase in 

 our knowledge of the life histories of the algae been considerable, 

 but the discovery of many new genera and species has made clear 

 the affinities of various families as never before. Of the 275 good 

 genera now recognized among the green algae, one fourth have been 

 discovered and described since the appearance of Engler and Prantl's 

 " Pflanzenfamilien " — the last complete work on the subject and still 

 the recognized authority. The addition of so many new and in 

 many cases important links to the chain of development of these 

 plants, has reduced the former chaotic condition to something like 

 order and it is no longer quite such a matter of speculation regard- 

 ing the origin of the main group of the green algae. 



Ten years ago Chodat derived the green algae from the simplest, 

 unicellular, non-motile forms then known, namely, the Palmellaceae. 

 Within this family he included four genera whose simple life his- 

 tory showed three principal stages. From these so-called " condi- 

 tions," as Chodat pointed out, developed the three important and 

 ruling tendencies which have dominated the lower green algae. 



These are: (i) The zoospore condition, or the unicellular motile 

 stage, with the other two conditions transient or subordinate. (2) 

 The sporangium condition, that is, the unicellular no;;-motile stage, 

 with the other two conditions accidental or transient. (3) The 

 tetraspora condition, where the non-motile cells are connected at 

 right angles by the increasing consistency of the walls, giving rise 



