INTRODUCTION TO CEYPTOGAMIG BOTANY. 141 



114. The species of this group are very widely distributed; a 

 species of Nostoo, or according to received nomenclature, Hor- 

 mosiphon, abounds to such a degree in the Polar regions, that 

 it affords a welcome food, consisting as it does of a modification 

 of cellulose, without any deleterioiis admixture. The species 

 is produced upon the soft and almost boggy slopes bordering 

 on the sea, but is carried about by winds ia every direction, 

 rolling over the surface of the ice and snow, and affording 

 a nidus for Podurce, and a little spider, Desoria arctica* It 

 has been found at a distance of ten miles from the land ; each 

 plant lies in a small depression ia the snow upon the ice. It 

 proved far more palatable than the true Tripe de roche, as 

 was indeed probable from the extensive use which is made 

 by the Chinese of an aquatic species Nostoc edule, Berk, and 

 Mont., which is dried, and forms an ingredient in their soups. 

 Two species, the common Nostoc, which in the northern hemi- 

 sphere occurs as far south as the Canary Isles, and also in 

 BoUvia,and N. microscopiwm,, Carm., were found by Dr. Hooker 

 in Kerguelen's Land : both on wet rocks, near the sea. Dr. 

 Thomson found several species in the salt lakes of Thibet, 

 floating on their surface, and attaining a considerable size, or 

 on the marshy brackish ground. The genus also appears in 

 French Guiana. A very splendid Sphcerozyga occurred in the 

 Antarctic regions, and the warm springs of India are not 

 without their representative. The species of Sphcerozyga 

 which occur in such situations are often used as an outward 

 application for glandular affections, and it is possible that they 

 may have some effect, since Henry observed that they contain 

 minute quantities of an alkaliue iodide. 



115. It has been asserted that these productions are nothing 

 more than states of lichens, a doctrine to which, however, I can- 

 not subscribe ; for though it is true that the fronds of the CoUe- 

 mal lichens do contain gonidia arranged m little necklaces, this 

 appears to be a mere case of analogy. The only difference, 

 indeed, which exists between ordinary Lichens and CoUemals, 

 is the pr&valence of the gelatinous element, and probably as a 

 consequence the greater adherence of the gonidia. The masses 



* Sutherland, Journal of a Voyage in Baffin's Bay, p. cxciv. 



