GELATINOUS, CRUSTACEOUS, AND STONE-LIKE ALGJ2. 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 Algse. 
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 Algse 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 Algse 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, 
