Mr. J. Ralfs on the mode of growth in Oscillatoria. 39 



in Stephens's collection ; the descriptions in his works however are 

 not taken from these specimens, but borrowed from Denny. 



Euplectus Kirbii, Denny, of which I have examined the original 

 specimen in the British Museum, is not identical with E. signatus, 

 as Erichson and Aube suppose, but with E. Fischeri, Aube (Tischeri, 

 Heer). Denny has overlooked the pit in the forehead which charac- 

 terizes this species. 



Stephens refers the Euplectus sanguineus, Denny, as a synonym 

 to E. minutus of Marsham, but incorrectly ; the specimen of the latter 

 differs in nothing from an ordinary E. signatus. 



E. ruficornis, Ste., is synonymous with E. ambiguus, Reichb. 



Bythinus grandipalpus , Ste., is the female of B. Curtisii, Denny. 



Bryaxis assimilis. Curt., I have not seen. 



The specimen named Bryaxis insignis, Reichb., in Stephens's 

 collection, does not agree at all with the true P. insignis, Reichb. 

 (=^Tyrus mucronatus), but is the same insect as Bryaxis juncorum. 



VI. — On the mode of growth in Oscillatoria and allied genera. 

 By John Ralfs, M.R.C.S., Penzance*. 



The growth of the lower Algae by repeated transverse division of 

 their cells is now a well-established fact. In the Desmidiecs and 

 the PalmellecE this division is usually complete and gives rise to 

 distinct individuals. In the latter family the common gelatinous 

 matrix mostly retains them in such close connection that the 

 entire mass is regarded as a frond, of which the cells are only 

 portions. The case is essentially similar in the Desmidiea ; but 

 in them the common matrix is so exceedingly thin that it can 

 scarcely be detected, whilst the slightest touch scatters the cells, 

 rendering their independence apparent, and hence each individual 

 is considered a frond. 



In Tiresias and many other simple, filamentous Algse, the 

 divided cells remain closely united, and form a jointed filament 

 which continues to elongate until the cells cease to divide. 



I believe that in Oscillatoria we may trace a mode of growth 

 of an intermediate kind and connecting these extremes. In many 

 species of this genus the stratum spreads with great rapidity. 

 This rapid growth cannot be caused by zoospores or granules 

 vegetating in constant succession, because, although the fila- 

 ments vary in length, their breadth is uniform. It does not de- 

 pend on the simple elongation of the filaments, because, in many 

 species, the filaments always remain short, notwithstanding the 

 great increase of the mass. 



The difficulty of tracing the growth in Oscillatoria is enhanced 

 by its cells being frequently confluent, or having their divisions 



* Read before the Botanical Society of Edinburgh, December 14, 1848. 



