THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY, 



[SECOND SERIES.] 

 No. 29. MAY 1850. 



XXIX.— O/i the Nostochine^. By John Ualfs, M.R.C.S., 

 Penzance*. 



[With two Plates.] 



Frond gelatinous, containing simple, jointed, generally monili- 

 form filaments. Some joints enlarged, all finally separating. 



The Nostochinece. may be regarded as a tribe of freshwater and 

 terrestrial Algse, for only a very few of its species are either lit- 

 toral or inhabitants of brackish waters. They are allied on the 

 one hand to the Oscillatorice and on the other to the PalmellecB ; 

 but I consider they have a closer affinity to the former than to the 

 latter. Some species of Nostoc, to the naked eye, have considerable 

 resemblance to fronds of Rivularia. Without the use of the mi- 

 croscope we are sometimes unable to distinguish Trichormus and 

 Sph(Brozyga from Oscillatoria, and even with its assistance the 

 young filament in Spermosira is liable to be regarded as an 

 Oscillatoria. So closely too is this family allied to the PalmellecBy 

 that some distinguished naturalists have united them. Hormo- 

 spora in the latter scarcely differs from it except by its uniform 

 and more distant cells. 



In the Nostochinece the filaments are always imbedded in gela- 

 tine. In Nostoc and Hormosiphon this gelatine is very evident, 

 and, especially in the young plant, is comparatively firm. It is, 

 indeed, often fieshy or even cartilaginous, and externally is always 

 condensed so as to form a distinct covering or epidermis (gene- 

 rally smooth and glossy) which limits the frond and gives it a 

 definite form. In Trichormus and the remaining genera the plant 

 forms a stratum of no determinate form or extent. 



In all the genera the filaments are simple, jointed and usually 

 moniliform, and finally break up into single joints. Their joints 



* Read before the Botanical Society of Edhkburgh, April, May, June and 

 July 1 819. 



Ann, ^ Mag. N. Hist. Ser. 2. Vol. v. 21 



