294 Transactions.—+Botany. 
advanced a certain distance will, without any discoverable cause, suddenly 
reverse the direction and retrograde. It is a very interesting sight some- 
times to watch these minute organisms in their advance across the field 
of the microscope. I have seen in QO. tenuis the two or three end cells 
waving backwards and forwards slowly and deliberately as though the fila- 
ment were feeling its way across the field of view. On meeting an obstacle, 
such as another Alga, the filament would halt as though it were investigating 
the nature of the obstruction—if the Alga happened to lie at an acute angle 
the Oscillatoria would accommodate itself and move along the side in contact 
with it; if, however, it lay at a right angle, it would, after a short exami- 
nation, pass either over or under it, and continue its onward march, or 
occasionally begin to move backwards, and so retrace its steps. In one 
specimen the terminal cell was surmounted by a short bristle, which was 
used apparently as a feeler. The singular deliberative motions I have 
attempted to describe, I have never seen except when the filament was 
moving forward; they do not seem to occur when it is performing a move- 
ment of retrogression. 
Oscillatoria, sp.n.? The usual method of reproduction in this genus 
is stated to be by the breaking up of the filaments, each articulation 
of which then takes upon itself the functions of a gonidium. I believe, 
however, they do sometimes emit spores, though I have not had an 
opportunity of watching them after their detachment from the parent 
filament. And in one instance—a specimen occurring as a purple stratum 
on a damp stone, which I have not been able to specify—there appears 
‘to be a series of special sporiferous cells, amongst, but quite distinct from, 
the ordinary articulation. (Fig. 5.) 
Lyngbya, common. 
Polypothrix distorta (?). 1 do not feel sure of this species, as I have 
seen only a single specimen. 
Nosrocuacez. 
Nostoc commune, M. Dic., 4. : 
ra verrucosum, H,, Ixxvi. 
Unvacez. 
Enteromorpha usta H., lxxvii; M. Die., 5. 
Ulva bullosa, — Ixxviil. 
” crispa, i.¢ lxxviii. 
Tetraspora (lubriea?), H., xxviii. 
- PaLMELLACEx, 
—— rupestris, M. _ 3. 
