108 
OSCILLATORIACEiE. 
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 
