CALCAREOUS ALGAS—MACKAY. xcill 
They are soon bleached white by exposure to light, and after being 
dried become very brittle, the articulations falling apart. In. addition 
to the red coloring matter there is a large amount of lime laid up with 
the tissue of each articulation, so that we have here plants which secrete 
lime from the sea water as the coral does among animals. Dilute 
hydrochloric acid applied to a portion of one of these fronds well 
covered with glass to protect the microscope, will show under a low 
power a rapid evolution of carbonic acid gas until the articulations of 
the frond become translucent, when all the lime is dissolved out of the 
vegetable tissue. 
The genus Melobesia appears as small, thin, more or less circular 
incrustations of lime filled tissue on other alge, generally. Thin 
incrustations on stones taken for Melobesia Lenormandii of Farlow are, 
probably, forms of Lithothamnion compactum. 
The genus Lithothamnion forms larger incrustations, of a red or 
purple color before they are bleached, some of the species rising into 
minute nodules or tubercles, and others rising even into rudely branch- 
ing coral-like masses. The name, from /ithos a stone and thamnion a 
little bush, was suggested by the latter habit. The reproductive organs 
of all these are in conceptacles, small spherical cavities, either immersed 
in the general frond or rising out of it. They are difficult to section 
for microscopic examination, for if the calcium carbonate is dissolved 
out of the tissue by, say, dilute hydrochloric acid, no matter how gently 
it is done, the tissue is more or less disorganized so as not to show the 
minute parts distinctly. And the sectioning of the undecalcified plants 
is very severe on the razor or other cutting apparatus. 
The two species of Farlow’s Marine Alge of New England, LZ. poly- 
morphum and L. fasiculatum, the tubercular or lobular, and the 
branching species respectively, 5 above being the most distinctive of the 
latter, are found all along the coast. But from the studies of M. Foslie, 
of Trondhjem, Norway, these two general forms may be found to cover 
several distinct species. Probably the following more exact species are 
represented under these forms :— 
Lithothamnion fruticulosum, (Kutz.) Foslie, f. typica, Foslie, the 
most conspicuous branching form. Next to it comes 
L,. colliculosum, Foslie. Then comes 
L. glaciale, Kellm. 
L. compactum, Kellm. And possibly, 
L. conscriptum. 
