108 OSCILLATORIACE^. 



more species of this genus. Others occur in lakes, and sometimes in such abundance 

 as to impart a blue-green tint to the water, over very wide areas. Others, again, inhabit 

 mineral springs and thermal waters ; and some are found on the damp surface of the 

 soil, especially in the autumnal months. Varied as are the habitats, the general 

 characters of the species are very uniform : and all are remarkable for an oscillating 

 movement of the filaments, from side to side, like the motion of a pendulum. This 

 continues with greater or less vividness, while the plant lives : but some species exhibit 

 much more lively movements than others, and all appear to be more active in warm 

 than in cold weather. 



A considerable number of species have been described by authors, but they require 

 to be studied in a living state, or at least with very perfect materials and an ample 

 suite of well preserved specimens. I cannot undertake to name specifically the few 

 scraps of American Oscillatorice which have been sent to me by various correspondents. 

 Probably most of the European species will be met with in America ; and no doubt 

 some others peculiar to the New Continent. It would be interesting to know whether 

 any species be found in the Mammoth Cave of Kentucky, or in other anomalous 

 localities. 



VI. MICROCOLEUS, Desmaz. 



(Chthonoblastus, Kiitz.j 



Filaments minute, rigid, straight, annulated, bundled, and enclosed within membra- 

 naceous simple or branching sheaths, which are either open or closed at the upper 

 extremities. 



The filaments in this genus have the structure of those of Oscillatoria or Calothrix, 

 but are developed within membranous common sheaths, which are either simple or 

 branched, and either lie prostrate in indefinite strata, like those of an Oscillatoria ; or 

 stand erect, in toothlike tufts, like those of many Calothrices. In all cases the sheath 

 is much attenuated at the base, gradually widening upwards, and terminating either in 

 an open, trumpet-shaped upper extremity, or in a closed club-shaped one. In the 

 lowest part of the sheath there is but a single longitudinal filament ; a little way up, 

 two or three parallel filaments are found ; and the filaments gradually increase in 

 number in the upper and wider portions of the common sheath. Hence it may probably 

 be inferred that the mode of growth of the frond is by the continual longitudinal 

 division of the filaments ; the older ones, having once split, remaining unchanged at 

 base ; while their apices by another splitting give birth to other filaments, which 

 multiply in the same manner. Such a mode of growth would account for the form 



