M. G. Thuret on the Reproduction of certain Nostochineae. 7 



bell-glass to prevent evaporation. The filaments soon became 

 decomposed ; the heterocysts lost their colour, and were in part 

 detached from the sporanges. A great number of the latter 

 were also spoilt, and the spores which they contained vanished 

 without leaving a trace. But others were preserved without any 

 change of aspect. I continued to observe them with care, and 

 in the course of the month of September, I had the pleasure of 

 seeing the spore at last pierce the summit of the sporange, and 

 become developed into a new filament, in the following manner. 

 The spore, becoming elongated, lifted up a little piece of the 

 internal wall of the sporange, which it pushed before it. As 

 soon as it had made its way out, it began to exhibit septa, and 

 to change into a torulose filament, composed of three or four 

 joints, filled with very granular contents. The divisions of the 

 joints are at first rather indistinct, but become more and more 

 clear in proportion as new ones are formed. For rather a long 

 time the fragment of the wall of the sporange which has been 

 lifted up by the spore remains at the summit of the filament in 

 the form of a little cap covering the last joint (fig. 12). The 

 filament elongates simultaneously at both ends, but more rapidly 

 at first at that which is outside the sporange. The new joints 

 are of less diameter than those formed in the place occupied by 

 the spore, so that the young filament is slightly attenuated at 

 the extremities (fig. 13). By degrees, however, these differences 

 are effaced ; the joints, in multiplying, acquire dimensions more 

 and more equal ; their granules become less apparent, and the 

 resemblance of the new filaments to the old ones is at last 

 complete. 



I have subsequently discovered that this experiment succeeds 

 just as well, or still better, with specimens dried and preserved 

 for several months in the herbarium, provided the spores are quite 

 ripe. On placing them in the same way on slips of glass with 

 a drop of water, I have seen them begin to germinate in about 

 a fortnight. The spores of Anabaina therefore belong to that 

 category of reproductive bodies which M. Al. Braun* calls hypno- 

 spores, and which are susceptible of development after a long 

 period of repose, and in spite of prolonged desiccation. In 

 many freshwater Algae we find reproductive bodies provided with 

 this persistence of vitality, which seems to be a condition neces- 

 sary for the preservation of the plants during the alternations 

 of drought and humidity to which they are exposed ; but none, 

 I think, are better endowed in this respect than the species of 

 Anabaina, as the following example will show. 



In the month of April 1848, I gathered fine specimens, well 

 in fruit, of Anabaina licheniformis, Bory (Cylindrospermum 

 * Algarum unicell. genera nova, p. 16. 



