Polymorphism 19 



mere stages in the growth of higher forms. It is necessary, how- 

 ever, to remark that a great many loose statements have been made 

 on this subject, statements which are supported by no direct or 

 conclusive evidence. Most bf the remarks have been based upon the 

 fact of the occurrence together, in one matrix, of various stages of 

 different plants, and to the assumed identity of certain normally 

 unicellular plants with unicellular stages in the life-history of 

 higher organisms. Undoubtedly in the case of the Myxophyceae 

 many different forms are met with in one gelatinous matrix, and 

 these are of the most confusing nature. Many of the higher blue- 

 green Alga? do certainly pass through stages which resemble very 

 much some of the so-called unicellular species, but there is equally 

 no doubt that careful observation frequently proves that this is a 

 resemblance and not an identity. In some instances it may be quite 

 true that a blue-green form which has been accepted as a species 

 in the past is really a stage in the development of another form, but 

 that does not necessarily prove that every blue-green Alga exhibits 

 wide polymorphism and that every form met with is only one stage 

 in some complex life-history. Similarly, in the Chlorophyceae, 

 polymorphism is frequent, but because species of Chcetophora or 

 Myxonema (Siigeoclonium) at one period of their existence regularly 

 and normally break up into ' Palmel la-like ' forms, it does not 

 follow that every aggregate of unicells such as Glceocystis, Palmella, 

 etc., is merely a stage in the development of Ghcetophora, Myxonema, 

 or some other allied plant. The observation of the polymorphism 

 of higher and lower types of Algae, both in nature and under 

 cultivation, is, however, the surest and best way to discover their 

 affinities, and in many cases furnishes direct evidence as to the 

 phylogeny of the plants in question. Thus, the fact that Myxo- 

 nema assumes under certain conditions a ' Palmella-siate,' much 

 resembling species of the genus Palmella but in no way specifically 

 related to them, is one of the primary reasons for regarding 

 Myxonema (and therefore the Chastophoracese) as having been 

 derived from the Palmellace*. 



Without question many of the Alga3 referred to the order 

 Protococcoidese have a much more direct relationship with fila- 

 mentous green Algae, particularly with the Chsetophorales, than is 

 indicated by their present systematic position. As an instance, 

 the genus Stichococcus, described by Nageli as a unicell, un- 

 doubtedly belongs to the family Ulotrichacea? and is connected by 



22 



