58 University of Calif urniu Puhlioations in Botany [Vol. 8 



16. Oscillatoria Gomont 



Trichomes free, often forming into dense tangled masses, cylin- 

 drical, without a sheath, or at times with a delicate, more or less 

 mucous sheath, smooth or constricted at the partitions, not moniliform, 

 straight or arcuate, not spirally twisted; apices straight or uncinate, 

 more or less tapering, terminal cell of some species with thickened 

 membrane. 



Gomont. Faut il dire Oscillatoria on Oscillaria, 1891, p. 273. 

 Oscillatoria Vaucher, Hist, des Conferv., 1803, p. 165 (lim. mut.). 



Gomont (1891, p. 273) has apparently discussed the generic name 

 and its relation to Oscillaria so thoroughly as to demand no especial 

 consideration here. As used at present and generally accepted its 

 limits are considerably changed from those proposed by Vaucher. 

 The type of the genus seems clearly to be Oscillatoria princeps Vaucher 

 {loc. cit., p. 190) arid the type locality (of this species) is Crevin, 

 near Geneva, Switzerland. Of the other eleven species assigned by 

 Vaucher to this genus Gomont (1893, pp. 256-266, Repr.) lists nine 

 as doubtful, and two, one each, to be referred to the genera Beggiatoa 

 and Microcoleus respectively. 



Oscillatoria is a genus containing somewhat over one hundred 

 recognized species, the great majority of which are inhabitants of 

 fresh water or growing in moist situations. The species usually listed 

 in a marine flora are largely, at least, to be found in brackish water 

 and consequently in the pools or other bodies of water in salt marshes. 

 In such situations the water is warmed by the air and by the sun and 

 is of decidedly higher temperature than that of the adjacent ocean 

 or larger body of strictly salt water. 



The species of Oscillatoria are to be distinguished from those of 

 Phormidiiim and of Lynghya by being destitute of a sheath and, in 

 general, this method of distinguishing them is both certain and satis- 

 factory. Certain species seemingly of Oscillatoria, however, show 

 (or develop?) a sheath under certain circumstances (especially 0. 

 sancta and 0. limosa) while the trichomes of Lynghya, and even more 

 so those of Phormidimn, escaping from the sheatli, take on for a time 

 exactly the appearance of being trichomes of Oscillatoria. The naked 

 trichomes of certain species of Phonniditmi as well as those of Micro- 

 coleus, not only imitate the appearance of trichomes of Oscillatoria 

 but also possess the power of movement characteristic of certain species 

 of Oscillatoria. 



