BOTANY : MARINE ALQJE. 99 



in the Boston market. Smaller filamentous species such as Ceram- 

 ium riibrum and several Polysi}>honice also are found in pools. A 

 very abundant red alga is Polysiphonia fastigiata, which forms 

 dense, rather rigid tufts on Axcophyllum nodosum which do not 

 ■collapse when left exposed by the tide. The color of this species 

 is, however, almost blacli, and at first sight it would hardly pass 

 for one of the red seaweeds. The calcareous red seaweeds are 

 represented on our coast by CoralUna officinal is and several species 

 of Melobesia and Lithothamnion. The Corallina is common in 

 deep pools and is at once recognized by its calcareous structure 

 and pinnate, jointed fronds. Most of the Melobesiae form small 

 crusts on other algae and the more solid Lithothamnia form pink- 

 ish, stony crusts on rocks and shells, often of considerable extent, 

 and either smooth or rough with solid tubercles. 



The green algtt belonging to the Chlorophyceoe reach perfection 

 in mid-summer, whereas most brown and red seaweeds mature at 

 other seasons. The green algie are most common in the higher 

 pools, even in those where the water is merely brackish or almost 

 fresh. Those of any size may be classed in two groups : the 

 Ulvaceae or sea lettuces, found everywhere on wharves, exposed 

 flats, and high pools, forming large flat expansions or inflated 

 intestine-like fronds ; and the filamentous species belonging to the 

 genera, Cladophora, Chsetomorpha and Rhizoclonium. It is 

 hardly possible to specify any of the common forms of this group 

 since the distinctions depend largely on microscopical characters. 



The algae are not the only plants of interest to the visitor to 

 our rocky coast. The maritime saxicolous lichens are very strik- 

 ing to the naked eye but the species are not especially character- 

 istic of the coast. There is one very abundant lichen, however, 

 Verritcaria mucosa, which grows on rocks at low tide. It is only 

 necessarj- to lift up the hanging masses of Fuci to find the rocks 

 beneath covered with the large, dark green patches of the Verru- 

 caria in company with the crustaceous red algae, Hildenbrandtia 

 and Petrocelis. On the exposed cliffs of the shore will be found 

 fine specimens of the orange colored Placodium elegans with other 

 species of the genus, Lecanora rubina, Rinodina oreina and other 

 crustaceous forms. The branches of the stunted trees and shrubs 

 near the shore are brilliantly colored with quantities of Thelo- 

 schistes chrysophthalmtis and T. parietinns, common species to be 



