MONORMIA. 231 



rence, and the definite position they occupy, seem to show 

 that they have some prominent office. 



The Nostochinae are chiefly found in fresh-water streams, 

 and in damp places and ditches. Very few are found in the 

 sea, and these only along the margin of the tide, on the heaps 

 of decaying Algae. Several occur in ditches of brackish water, 

 and these are admitted into the present work. All the kinds 

 we have here to notice are of very minute size, but some of 

 the fresh-water kinds and those found on damp soil have 

 fronds of large dimensions. The gelatinous substances often 

 seen late in autumn on damp garden- walks, and called "fallen 

 stars," a name derived not from their lustre but from the sud- 

 denness of their appearance, are species of the genus Nostoc. 

 These dry up into mere films in dry weather, and expand 

 again after the first shower, so that they are not always so 

 suddenly produced as they appear to be. The structure of 

 these Nostocs is simpler than that of the species of Collema, 

 among Lichens, but there is much affinity between these 

 plants ; and through Nostoc the passage from the Algae into 

 the Lichens is thus clearly established. 



SYNOPSIS OF THE BRITISH (MARINE) GENERA. 



I. MONORMIA. A single moniliform filament included 



within a spirally twisted and convoluted gelatinous 

 frond. 



II. SPH^ROZYGA. Filaments free, moniliform, usually des- 



titute of an evident sheath. 



III. SPERMOSIRA. Filaments free, moniliform ; each en- 

 closed 



tube. 



I. MONORMIA. Berk. [Plate 27, A.] 



Frond branched, composed of a single, moniliform thread, 

 following the convolutions, immersed in gelatine. Berk. 

 Name, /AOVOJ, one, and of/noj, a necklace. 



1. M. intricata, Berk. GL Alg. p. 46, t. 18; Harv. Phyc. 

 Brit. t. cclvi. 



