M. G. Thuret on the Reproduction of certain Nostochineae. 3 



new joints, which subsequently divide in the same way. As to 

 the large globules, they do not divide, and they end by becoming 

 detached from the chaplets without undergoing any change. 

 They have long been regarded, though without any reason, as 

 the reproductive bodies of Nostoc. M. Kutzing even still con- 

 tinues to designate them by the name of spermatid. But this 

 denomination, which M. Kutzing, by a lamentable abuse, applies 

 indifferently to most diverse organs, cannot be longer preserved 

 here, any more than in many other cases where there is nothing 

 to justify its employment. Among the different names that 

 have been given to these large joints of the Nostochinea, that 

 of heterocysts, employed by Dr. Allman, seems to me the most 

 suitable; and I shall adopt it the more willingly as it does not 

 prejudge the function, of whose true nature we are at present 

 ignorant. 



It is during the months of September and October that we 

 observe in Nostoc vesicarium the same series of phenomena that I 

 have described in Nostoc Mougeotii. We at that time frequently 

 find individuals whose contents escape in a diffluent greenish 

 jelly, which spreads over surrounding bodies. This jelly pre- 

 sents exactly the aspect of a Palmellacean. But if a portion is 

 placed under the microscope, we perceive that it is filled with 

 fragments of chaplets intermixed with detached heterocysts. 

 An attentive examination of these fragments of chaplets shows 

 that at this epoch they are endowed with a creeping motion, — 

 very slow, but easy to ascertain under a sufficient magnifying 

 power. Placed in a drop of water, on a slip of glass, in front 

 of a window, they gradually gather together at the margin of 

 the drop nearest to the point whence the light comes. When 

 one of these deliquescing Nostocs is placed in a saucer with a 

 little water, the chaplets soon spread round the circumference, 

 and form at the bottom of the saucer a greenish pellicle, as an 

 Oscillatoria would do*. 



If the observation of the fragments of the chaplets be con- 

 tinued for some days, they are soon seen to become motionless, 



* The independent motion possessed by the chaplets of the deliquescing 

 Nostoc did not escape Vaucher (Conferves d'eau douce, pp. 215, 216). It 

 is especially evident in the aquatic species. At least, it appeared to me 

 very marked in Nostoc Mougeotii, and Vaucher has made the same obser- 

 vation on Nostoc verrucosum. But it occurs also under the same circum- 

 stances in the terrestrial species, and I was in error in my former paper in 

 raising some doubt upon this point. I have had particular opportunity of 

 ascertaining it in fine specimens of Nostoc commune, gathered in warm 

 damp weather in the month of June, when some portions were beginning 

 to deliquesce. I mention this fact, because it was under the same con- 

 ditions and at the same time of the year that Vaucher also observed the 

 movement of the chaplets in this species. 



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