140 Ulothricaceae and Chaetophoraceae 



viction that it is the only course based on rational principles and 

 offering a fair hope of attaining the goal of stability. How little 

 disturbance this method makes in these groups is seen in the fact 

 that it has appeared necessary only in two cases to displace the 

 names current among modern algologists, namely, Conferva and 

 Stigcocloninm. 



Very few varieties have been listed, because experience has 

 proved that many of those in current use are either mere growth 

 forms of the species with which they are associated, or are wrongly 

 associated with the species. Mr.Wolle was in the habit of listing all 

 the varieties given by Rabenhorst and Kirchner, without reference 

 to their actual occurrence in this country. These have been repeated 

 by De Toni as American forms, and thus confusion has arisen. 



A sharp distinction between variety and forma, in the technical 

 sense, has been here understood : by the term variety, better 

 called subspecies, is indicated a form which is well-marked in re- 

 lation to the species. and fairly constant in character ; by the term 

 forma we have designated a form which is sufficiently well marked 

 to demand recognition, but which is regarded as probably only a 

 growth state of the species. 



The limits of the two families treated are drawn practically on 

 the lines laid down by Wille in Engler & Prantl, Die naturlichen 

 Pflanzenfamilien. The chief departures from that work are the 

 relegation of Trentepohlia and Acroblaste to a separate family, be- 

 cause of their specialized sporangial cells, and the removal of 

 MicrotJiamnion from this group to what is clearly its proper place, 

 among the Chaetophoreae. As a matter of convenience we have 

 also arranged the microscopic genera of the Chaetophoraceae in a 

 separate tribe, the Herposteireae, taking the name from the most 

 highly developed of the group, a name which is at the same time 

 most suggestive of the creeping habit of all the forms. 



It is very probable that the position taken by Borzi ('89), 

 Bohlin ('97), and Wille ('01), in removing Conferva (= Tribo- 

 nema) from the Ulothricaceae to a separate family and order in 

 close affinity with the Ophiocytiaceae, is well grounded ; for 

 the present convenience, h wever, of American students who have 

 not distinguished this genus from Microspora, it has been tempo- 

 rarily retained in its old position. 



