CALCAREOUS ALG.E MACKAY. XC111 



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 algae, 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 lithos 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 Algse of New England, L. 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. glaciate, Kellrn. 



L. compactum, Kellm. And possibly, 



L. conscriptum. 



