(14) 



with a periphery composed of small romidish cellules, arranged in 

 simple moniliform series ; vesicles contained in the branchlets, often at 

 the base of a receptacle, elliptical with thick walls. Substance cori- 

 aceous or subcartilaginous, and brittle when dry, not adhering to paper. 

 Colour, a bright olive-green when fresh, dark olive or almost black 

 when dry. 



This curious Alga seems to have been very properly separated from 

 the other species of the genus Fucus ; although agreeing with them in 

 external habit, it is considerably different in structure, being more closely 

 allied in this respect to the preceding genera. Like them also it seems 

 to be an ocean species, being confined to the south-west of England, and 

 south and west of Ireland, on the shores of the latter country being 

 rather plentiful, at least in several localities. 



The question of the geogi'aphical distribution of species, both of 

 marine and land plants, is one of great interest, and one well calculated 

 to repay the trouble of investigation. It is not unlikely that the fact 

 of so many of our rarer southern species being confined to the south- 

 west of England and Ireland, is referable to the warmer cun-ent of the 

 Atlantic from the south impingeing on these coasts, and thus keeping up 

 a higher temperature than the latitude would otherwise indicate ; on 

 this also may depend the fact that the Algae generally are more luxu- 

 riant in growth and more abundant in individuals as well as species on 

 the west than on the east coast of our islands. 



EXPLANATION OF PLATE CXXXV. 



Fig. 1. — Pycnophyciis tuherculatus^ natui-al size. 

 2. — Portion of a receptacle. 

 3. — Transverse section of same. 

 4. — Section of conceptacle. 

 5. — Spore. 

 6. — Filaments. All magnified. 



