10 



FRESn-WATER AhGJE OF THE UNITED STATES. 



b 



cellular plant in the stricter use of the term. Increase takes place by the multipli. 

 cation of cells by division, and also by the formation of enlarged thick-walled cells, 

 to wliich the name of spores has been given, although it is entirely uncertain 

 whether they are or are not the result of sexual action. There are numerous 

 peculiar forms of cell multiplication by division occurring ii; these plants, the dis- 

 cussion of Avhich will be found scattered through the remarks on the various 

 families and genera. 



The method of reproduction, and in fact the life history in general, of the phy- 

 cochroms, is still involved in such mystery, that I am not aware that absolute 

 sexual generation has been demonstrated in any of them. This being the case, it is 

 not to be wondered at that many have conjectured as possible, and some have roundly 

 asserted as true, that the phycochroms are merely stages in the life history of higher 

 plants ; that they are not species, and, consequently, that any attempt at describing 

 such is little more than a busy idleness. In regard to some of them it has certainly 

 been rendered very probable that they are merely fixed stages of higher plants. 

 On the other hand, in the great bulk of the forms, no proof whatever has been 

 given that they are such. They all certainly have fixed, definite characters, capa- 

 ble of being expressed and compared, so that the diff'crent forms can be defined, 

 recognized, and distinguished. If, therefore, future discoveries should degrade 

 them as subordinate forms, names will still be required, and definitions still be 

 necessary to distinguish them one from the other, so long as they are common 

 objects to the microscopist. 



If Nostoc commune, for example, were proven to be a peculiar state or develop- 

 ment of Polytricum commune, I conceive it would be still known as Nostoc commune. 

 But, as previously stated, no proof whatever has as yet been furnished for the vast 

 majority of the plants of this family, to show that they bear any such relation to 

 higher plants ; and until some such proof is forthcoming, certainly the only scien- 

 tific way to act, is to treat them as distinct species. 



Order CystipIlOrSC. 



Plantae unicellulares. CelluliB singute vel plures in familias consociatoe. 

 Unicellular plants. Cells single or consociated in families. 



In this order the cells are oblong, cylindrical, spherical, or angular. They are 

 sometimes single, or more commonly are united by a common jelly into families, 

 which sometimes are surrounded by distinct coats. The mucus or jelly, in which 

 the cells are imbedded, is mostly, but not always, colorless, and varies in firmness 

 from semifluid to cartilaginous. The division of the cells may take place either in 

 one, two, or three directions or planes. 



Family CHROOCOCCACEiE. 



Character idem ac ordine. 

 Characters those of the order. 



