244 



FAM. XIII. OSCILLATORE^E. 



The family of Oscillator ea, limited to the genera Oscillatoria 

 and Microcoleus, is one of the most distinct and remark- 

 able of the divisions of the Alga. The majority of the 

 species are characterized by the minuteness of their fila- 

 ments, the equality of their calibre, and their mathematical 

 rectitude or straightness ; they are still further distinguished by 

 the brevity of their cells, the ease with which these separate 

 from each other, the wonderful rapidity of their growth, the 

 surpassing brilliancy of their colours, and lastly, by a peculiar 

 oscillation, upon which feature their generic name has been 

 founded, but with regard to which I can myself perceive 

 nothing extraordinary, although the phenomenon is certainly 

 peculiar to this family nothing indicative., as most suppose, 

 of a sensitive or animal life. The explanation to be given 

 of this oscillation of the filaments I consider to be partly of 

 an external, and entirely of a physical character. It has been 

 stated that the filaments of very many species of Oscillatoria, 

 and indeed of all those which present the phenomenon of 

 oscillation, are remarkable for their straightness or rectitude, 

 which is due to a certain degree of elasticity belonging to 

 them, and which leads to the effort on their part, whenever, 

 as on being placed for observation on the field of the micro- 

 scope, must be the case, they are bent or put out of a straight 

 line, to recover that position which is natural to them. This 

 elastic property of the filaments, currents almost impercep- 

 tible in the liquid in which they are immersed, and perhaps 

 unequal attractions amongst the filaments themselves, are 

 causes amply sufficient to explain any motion which I have 

 ever witnessed amongst the Oscillatoria, and which motion I 

 cannot help thinking to have been misunderstood and exag- 

 gerated to such an extent, as to throw around these plants an 

 unnecessary degree of mystery. 



