2 M. G. Thuret on the Reproduction of certain Nostochinese. 



confirmed by Dr. Montagne, in a note published by him last 

 year on Nostoc Boussingaultii*. For my own part I have re- 

 peated, some years since, on a terrestrial species common about 

 Cherbourg, all the observations I formerly made upon Nostoc 

 Mougeotii. In spite of the difference of station of the two 

 plants, they were reproduced exactly in the same way, and pre- 

 sented exactly the same phenomena. The resemblance in this 

 respect is so complete, that, finding no new fact demanding no- 

 tice, I have thought it useless to publish these researches. If 

 I determine to do so now, it is above all from a desire to profit 

 by the talent of M. Riocreux to illustrate the subject by figures 

 far more perfect than those which accompanied my preceding 

 memoir. In the second part of this note I shall make known 

 a mode of reproduction of another genus which offers a certain 

 resemblance of structure to Nostoc, but which possesses a distinct 

 fructification, of which the latter is destitute. 



I. 



Nostoc vesicarium, DC, is a small species with a globular 

 frond, growing on the ground among mosses and blades of 

 grass. It is met with abundantly around Cherbourg, on the 

 coping of walls covered with earth, along turfed roads, &c. 

 Young specimens are perfectly spherical, often combined in 

 great numbers under the form of little grains of a blackish-green 

 colour, the dimensions of which vary from microscopic minute- 

 ness to the size of a pea. In proportion as the plant enlarges, 

 its frond becomes less regular; it produces convolutions and 

 folds, and the largest specimens form sinuous expansions, re- 

 sembling small specimens of Nostoc commune. 



Under the microscope the frond presents the same structure 

 as that of other species of Nostoc. It consists of a transparent 

 gelatinous mass, smooth and firm externally, sometimes having 

 a yellowish tinge at the borders, while within are entwined 

 innumerable chaplets of greenish granules. These chaplets are 

 simple, and are composed of an indefinite series of globular 

 joints, formed of a slightly granular pale green substance. The 

 row is interrupted at intervals by a larger globule, almost colour- 

 less or slightly yellowish, with contents more homogeneous and 

 less refractive than those of the other joints : on each side of 

 this globule is observed a little granulation situated at the point 

 of contact with the adjacent joint (PL I. fig. 4). The chaplets 

 are elongated by the repeated division of the green globules. 

 Each of these, after having increased a little in the longitudinal 

 direction of the row, is cut in half, and thus gives birth to two 



* Note sur deux Algues nees pendant les experiences de M. Boussin- 

 gault, Coraptes Rendus, 1856, April 28. 



