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



marked merely by faint transverse strise. Still that the cells 

 divide as in the other simple Algse will scarcely be contested^ if 

 indeed the fact be not sufficiently proved in those species which 

 have some of the striae about twice the ordinary distance apart, 

 as is always the case when cells are dividing. 



In general the cells are indicated, as I have just stated, by 

 more or less evident transverse, straight striae; but at certain 

 intervals the junction margins become rounded during division 

 and the filament separates into distinct portions. All the Oscil- 

 latorieae have the filaments inclosed in sheaths. When the sheath 

 divides together with the cell, the original filament at once forms 

 two ; and as this process is continually going on, we can easily 

 conceive the rapid extension of the stratum consequent upon the 

 progressive increase in the number of filaments. 



It may be necessary to mention, that it is easy to distinguish 

 between a natural separation and a fracture. In the latter case 

 the ends formed by violence are abrupt ; in the former they are 

 usually rounded. 



When, as in some species, there is a complete separation of the 

 internal filament unaccompanied by simultaneous division of its 

 sheath, the latter retains the portions in connection. Lyngbya 

 ferruginea affords a good example of this kind, and as its fila- 

 ments are stouter than those of most species of Oscillatoria^ no 

 better plant can be selected for observation. If a portion of the 

 stratum be examined, filaments of various lengths may be seen 

 mingled together ; but they are all of the same breadth, although 

 some of them are not longer than broad. 



When separated portions are thus held together by the sheath, 

 there is generally a short interval between them. Whether this 

 results from an elongation of the sheath or the mutual repulsion 

 of the inclosed portions is doubtfuh The latter I consider as the 

 more likely cause. May it not be produced by an electric cur- 

 rent developed at the instant of partition ? Perhaps the radia- 

 tion of the filaments from the stratum, in some species of OsciU 

 latoria, may be similarly accounted for. 



Microcoleus is known by its numerous, short, simple Oscilla- 

 toria-Yik^ filaments being contained within either a simple or a 

 slightly branched, inflated sheath or frond. The presence indeed 

 of this common covering is the character which separates Micro-' 

 coleus from Oscillatoria ; for the filaments and their manner of 

 division are alike in both. 



In Oscillatoria the parted filaments are retained together 

 merely by the common mucus which permits a comparatively 

 wider range, and allows them to diverge in various directions. 

 In Microcoleus, on the contrary, their freedom is restricted; the 

 frond by its form and size keeps them parallel and binds them 



