VARIATIONS OF MOSSES. 31 



more or less imperfect development, or the nature of their 

 division, as in the Dicranei. 



From all these causes, the distinction of species requires 

 great caution ; and, after all that has been done towards reduc- 

 tion, it is still quite certain that much still remains to be 

 accomplished, and that many supposed species owe their dis- 

 tinctions merely to changes which arise from climatic condi- 

 tions or differences of habitat. 



