NOSTOCHINE^. Ill 



those in the neighbourhood of the heterocyst. Finally, at maturity, the threads break 

 up, and the enlarged brown cells are found to contain spores which germinate and 

 continue the species. They have been stated to change into zoospores, but this requires 

 confirmation. M. Thuret^ in a communication recently made to the Natural History 

 Society of Cherbourg (Aug. 1857, vol. 5) has described and figured the germination 

 of the S])ores o{ Anabaina Uchenifo7'mis, and ^4. major. In these species the sporan- 

 gium is oblong, and contains at maturity a deep brown solitary spore. M. Thuret 

 having obtained some specimens with ripe fruit, set them aside in a convenient glass 

 vessel, and observed them from day to day. The filaments soon broke up, the hetero- 

 cysts and sporangia floating apart in the water. Many of the latter perished, melting 

 away, and disappearing altogether. Some remained sound, and these were carefully 

 supplied with water, until germination commenced. The spore, in germinating, at 

 first lengthens, pushing against one end of the sporangium, which it finally pierces 

 lifting off the tip of the periderm like a lid, and thus its extremity issues, as the radicle 

 from an monocotyledonous seed, capped with the lid of the sporangium. At this period 

 new cells begin to be formed, by the repeated sub-division of the spore, which continues 

 to lengthen till it is transformed into a moniliform filament or string of cells, like that 

 from which it was derived. At first the divisions between the cells are but little 

 distinct, but they become more and more strongly defined as growth proceeds. The 

 filament lengthens at both extremities, but more rapidly at that which projects into the 

 ■water ; the young articulations are of smaller size than the rest, and thus the filament 

 tapers towards each end. But this character gradually disappears, and the cells acquire 

 a uniform dimension, proper to the species. M. TImrefs first experiments were made 

 with freshly gathered sporangia : but he afterwards succeeded in causing to germinate 

 specimens which had been dried and preserved for several months in the herbarium- 

 They began to germinate in about a fortnight. Others (of Anahaina Ucheniformis) 

 which had been kept for nine years in a dried state, germinated in an equal space of time, 

 and the experiment was repeated several times with like success. Several other fresh- 

 water Alga3 have been observed to possess the same property of revivification, and it 

 seems a necessary endowment to enable them to continue the existence of their species 

 through the alternate drying and moistening to which they are subjected in nature. 



To M. Thuret we are also indebted for observations on the ordinary propagation by 

 gemmation of the Nostocs, and for an account of the way in which the compound frond 

 is developed. In the autumnal months, when this process goes forward, the old ^"ostoc 

 may be said to diliquesce, the gelatine becoming loose and exuding, and the filaments 

 contained in it breaking up into small fragments. If these be collected and placed in 

 a glass of water, they may be observed to have a slow, progressive movement, like that 

 of the OsciUaiorice, which enables them to change their place ; and at length they 

 generally fix themselves on that side of the glass next the light. By continuing the 

 observations for some days, the broken threads are seen to become immoveable, and 

 then to be invested with a transparent pellicle. At the same time the green cells 

 increase in size, expanding laterally, till the thread attains nearly twice its ordinary 

 diameter. A cell division, in vertical order, then takes place throughout its component 

 cells, and thus the filament splits into two parallel filaments, which are then contained 



