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 0. temds 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 ceU 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.) 



Lynghya, common. 



Polypothrix distorta (?). I do not feel sure of this species, as I have 

 seen only a single specimen. 



NOSTOCHACE^. 



Nostoc commune, M. Die, 4. 

 „ verrucosum, H., Ixxvi. 



Ulvace^. 

 Enter omorpJia intestinalis, H., Ixxvii; M. Die, 5. 

 Ulva bullosa, H., Ixxviii. 

 „ crispa, H., Ixxviii. 

 Tetraspora (luhrica?), H., Ixxviii. 



Palmellace^. 

 Microhaloa rupestris, M. Die, 3. 

 Botrydina vulgaris, H., Ixxxi. 

 Coccochloris vulgaris, M. Die, 3. 

 „ protuberans, H., Ixxvi. 



