1920] Setchell-Gardner : Chlorophyceae 199 



The only differences in such cases are the usually more regularly 

 cylindrical segments of the species of Rhizaclo'iiium and the fewer 

 nuclei in each segment. Even these fail in some cases. From Ilor- 

 miscia, Chaetomorpha differs essentially in the characters of the zoo- 

 spores as indicated under the description of that genus. 



The genus Chaetanwrpha is credited with about fifty species, but 

 some of them will probably be found to be invalid. While we are able 

 to enumerate six species as having been found within our territory, 

 we feel certain that careful search will reveal additional species and 

 varieties. 



Chaetomorpha consists of attached, erect species and of horizontal, 

 entangled species unattached at maturity. It is possible that some, 

 at least, of the latter are simply states of the former. Such a relation- 

 ship is supposed to exist between Chaetomorpha aerea (Dillw.) Kuetz. 

 and C. Linum (Fl. Dan.) Kuetz. on the one hand, and C. melagonium 

 (Web. and Mohr) Kuetz. and the prostrate plant which has been 

 known as C. Picquotiana Mont, on the other. This relationship, how- 

 ever, has not been demonstrated by cultures but is inferred from 

 resemblances existing between the supposedly related states or species. 



The attached species of Chaetomorpha possess an elongated basal 

 segment which produces branched rhizoidal or even rhizome-like 

 processes of attachment from its lower end. These elongated basal 

 segments and organs of attachments distinguish these species of 

 Chaetomorpha from those of both Rhizoclonium and Hormiscia. 



The development of the prostrate species of Chaetoviorpha has not 

 been thoroughly worked out, but judging from what Okamura (1912, 

 p. 163) has found in Chaetomorpha spiralis and from what we have 

 observed in C. torta, the plants of these species are attached at first, 

 but probably never assume the erect and tufted habit of the other 

 group, very early assuming a prostrate and flexuous or crisped habit, 

 intertwining and becoming detached. It may be that they are states 

 of other species, but it also may be that \\\ey are distinct species or, 

 at least, varieties of the erect species they most naturally resemble. 

 Until more is certain along this line, it seems best to keep them distinct 

 and this policy will be followed by us. 



Key to the Species 



1. Filaments erect, solitary or tufted 2 



1. Filaments soon declined, becoming horizontal and entangled 5 



2. Filaments reaching a diameter of 300yu or more 4 



2. Filaments 300/x or less in diameter 3 



