NOBTOCHINE^E. 269 



tome ii., there are some interesting observations on the re- 

 production of Nostoc verrucosum by M. Gustave Thuret, of 

 whose accurate and skilful researches I have already had oc- 

 casion to avail myself in the Introduction. 



" When the plant has arrived at its full developement, the 

 external pellicle, formed by the thickened mucilage, breaks, 

 and permits the escape of the green jelly, which is composed 

 of mucilage and threads. These last scatter themselves in the 

 water the more easily, that they are endowed at that time with 

 a spontaneous motion, analogous to that of the DiatomacecK. 

 This curious phenomenon has been already observed by 

 Vaucher, who believed he had found it, although much more 

 evident in all the other Nostocs. In spite of the assertion of 

 that conscientious observer in spite of the earnestness with 

 which he sought to generalise this fact (Hist, des Tremelles, 

 p. 215. et suiv.), it is difficult to compare movements at least 

 equivocal, with mobility so evidently spontaneous, which the 

 threads of the Nostoc verrucosum possess. Perhaps it is not 

 without some interest to remark on this subject, that the 

 spontaneous movements, the locomotion, are again met with 

 under different forms, in the Algce, which, like the Nostocs, 

 live in running waters in the Oscillatoria, in the spores of 

 Vaucheria, the Confervece, &c., and that this faculty appears 

 to be a condition of their station. 



" To observe well this phenomenon in the Nostoc verru- 

 cosum, the most simple way is to place in a plate filled with 

 water some fine specimens freshly gathered. At the end of 

 two or three days the external skin breaks, the threads ex- 

 pand in the water, and form at the bottom of the plate, or 

 on the surface of the liquid, a green scum, nearly like that 

 of the Oscillatoria. If then you have recourse to the mi- 

 croscope, you observe that the threads, originally very long, 

 and winding in a thousand ways, are divided into a number 

 of fragments of unequal lengths, all nearly straight, or 

 scarcely bent, which move in the direction of their lengths, 

 and seem to creep upon the surface of the object glass. The 

 larger globules are detached and immoveable ; no increase 

 of magnifying power or mode of clearing, no re-agent, no 



