Remarks on a Variety of Nostoc Priinifoune . 253 



REMARKS ON A VARIETY OF NOSTOC PRUNI FORME. 



By Geo. B. Twitchell. 



(Read October 5, 1886.) 



Early last spring the Society received, under tlie name of 

 "Agates in an inception stage," a bottle of nostocs collected at 

 Haidley, Idaho. In .'\ugust I received another lot of the same. 

 This idea of the\r connection with agates is readily explained by 

 their appearance, for they surely bear both externally and internally 

 a marked resemblance to the agate pel)bles found in some of the 

 western streams. 



The various species of the genus nostoc are generally found 

 in water or damp places as more or less firm gelatinous masses. 

 These thalli vary for the different species, some being almost mi- 

 croscopic while others cover over a square foot of moist sand. 

 Some are indefinitely expanded, while others are restricted by a 

 sort of periderm to a more definite shape. 



Inside of these gelatinous masses will be found serpentine 

 rows of roundish cells, with here and there larger cells ot a differ- 

 ent color, called heterocysts. These filaments are usually, if not 

 always, inclosed in sheaths to which the heterocysts adhere by 

 their sides. The growth of these filaments is by a cell division. 

 According to Tluiret the reproduction is in this manner : The 

 thallus becomes softened and a green jelly escapes. This is made 

 up of detached portions of nostoc filaments that have straightened 

 out. These have an oscillaria-like motion. They are sensitive to 

 light, always accumulating at the brightest part of the vessel con- 

 taining them. In the development of one of these /lOf/iiogo/ies, as 

 they are called, the first change that takes place is the formation of 

 a distinct gelatinous sheath about the whole of the filament. 

 When this is formed the inclosed cells divide once or oftener, the 

 plane of the division being parallel to the original direction of 

 growth. The result is two or more rows of cells in a now rather 

 distended sheath. By a reuniting of these cells a single curved 

 nostoc filament is formed within a sheath which has now shortened 

 and widened to a more globose form. This young nostoc secretes 

 jelly and grows until it reaches the size of the parent. The exist- 

 ence of a reproduction by means of spores has been suggested by 



