1852.] Linnean Society. 167 



in large masses on the surface of pools and lakes in soils impregnated 

 with carbonate of soda, and of which heaps are drifted by the winds 

 upon their banks. It occurs as high up as 17,000 feet, and is of a 

 green or pale purple colour ; and this too appeared to Dr. Hooker 

 to belong to Nostoc commune. Samples of both were forwarded to 

 Mr. Berkeley, whose notes to the following effect were also laid 

 before the Society. 



Mr. Berkeley states that he has been unable to find any account 

 of the chemical constituents of Nostoc. The chemical condition of 

 such species as he has been enabled to examine, under the influence 

 of iodine and sulphuric acid, seems to vary not only in the different 

 species, but in individual specimens, and even in parts of the same 

 specimen. In some the gelatinous matter and the chains of 

 spores assume a more or less deep tint of violet, indicating that the 

 greater portion consists of cellulose, perhaps in some cases partially 

 changed to dextrine by the action of the sulphuric acid ; while in 

 other cases the prevailing tint is yellow-brown, indicating rather 

 bassorin. No purple tint occurs where merely iodine is used, and 

 the change therefore is not due to the presence of amylum. In fresh 

 specimens of Nostoc commune, the spores assume a beautiful green 

 tint, which is probably due to the combined tint of the yellow pro- 

 tein contents of the cells and the blue cellulose of which their wall 

 is formed. In the Arctic specimens and in English Nostoc commune 

 the bassorin tint prevails, while in specimens from Thibet (probably 

 Nostoc salsum, Kiitz.), gathered by Dr. Thomson, in pools of water 

 where the soil is covered with an efflorescence of carbonate of soda, 

 cellulose is indicated, but with every intermediate shade. Mr. Ber- 

 keley has, however, found that in woody fibres which in bleaching 

 have been exposed to salt water, a deeper purple tint is assumed than 

 when they have been bleached by rain water, so that something may 

 possibly be due to the peculiar place of growth of the Thibetan 

 species. In Nostoc edule the yellow-brown tint is stronger than in 

 any other specimen examined ; but it is scarcely probable that any 

 very constant chemical characters will be found to prevail in the 

 different species. In either case there would be a very nutritious 

 food, and one from its gelatinous condition probably easily assimi- 

 lated. The habit of the Arctic species is exactly that of Nostoc 

 commune, and Mr. Berkeley would not hesitate to regard it as iden- 

 tical, if there were no other difference than a little increase in the 

 relative size of the threads of spores ; but in parts of the fronds the 

 chains are surrounded by a distinct gelatinous envelope, presenting 

 an appearance somewhat similar to that of toad-spawn, which is very 



