'GELATINOUS, CRUSTACEOUS, AND STONE -LIKE ALG^E. 85 



or red tint during the process of drying, and assume a grey 

 appearance. An odour like that of violets is common to 

 all the species, and is particularly observable when large 

 quantities are brought together. However, colour and 

 smell must not be taken as characters of any great value : 

 the true distinguishing marks lie in the form of the cells, 

 and the ramification of the rigid filaments. 



The last of the three forms which I have grouped 

 together in this chapter embraces the stone-like Alga?. 

 This peculiar mode of growth may be seen in certain 

 species which have the property of separating carbonate of 

 lime from the surrounding water, and depositing it among 

 their filaments. This peculiarity imparts a hard stiff 

 appearance to the latter, so that to the uninitiated they 

 appear to be made of stone. In shape these Alga? are 

 usually semiglobose, and adhere tightly to stones, piles, 

 breakwaters, and similar submerged objects. Where they 

 can be taken off by hand, it is better to adopt that plan ; 

 but if fixed too closely for the fingers to be of any use, 

 recourse must be had to the hammer and chisel. The 

 specimens may be put away in a paper case ; or, if thin 

 enough, fastened on a sheet of stout paper with gum 

 arabic. 



Before the specimens can be examined under the micro- 

 scope, the carbonate of lime must be dissolved, as of course 

 its presence renders them opaque, even when very thin 

 sections are made. This can, however, be easily effected by 

 leaving the Algae for a sufficient time in dilute muriatic 

 acid. Indeed, common vinegar, though not so rapid in its 

 action, is just as efficacious. Bubbles of carbonic acid 

 begin to burst through the surface of the liquid, and so 

 long as this ebullition continues it is certain that lime is 

 still present. The gas having thoroughly escaped, the 

 preparation will be found in a flaccid condition, and suffi- 

 ciently soft to allow of very thin sections being cut from it 

 by means of a sharp razor. These should be forthwith 

 laid in a watch-glass and once more submitted to the acid, 



