THE ANNALS 
MAGAZINE OF NATURAL HISTORY. 
[SECOND SERIES.] 
No. 29, MAY 1850. 
XXIX.—On the Nostochiner. By Joun Ratrs, M.R.C.S., 
Penzance*. 
[ With two Plates. | 
Fronp gelatinous, containing simple, jointed, generally monili- 
form filaments. Some joints enlarged, all finally separating. 
The Nostochinee may be regarded as a tribe of freshwater and 
terrestrial Algze, 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 Oscillatoria and on the other to the Palmellee ; 
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 Zrichormus and 
Spherozyga 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 Palmellea, 
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 Nostochinee 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 fleshy 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 Edinburgh, April, May, June and 
July 1849. 
Ann. & Mag. N. Hist. Ser. 2. Vol. v. 21 
