LAURENCIACE^. il9 



like regularity, and are always alternate to each other, 

 and opposite either to a conceptacle or to a branch, 

 and the brilliant colour and cellular structure of the 

 frond, are the most obvious characters. Only floating 

 or cast-up specimens of this species are usually to be ob- 

 tained. It is annual, and grows on rocks at and beyond 

 low-water mark, during summer and autumn. 



Genus XLIV. LAURENCIA. 



T'rond solid, cartilaginous, cylindrical or flattened, pin- 

 nately-branched, composed of two strata of cells ; those in 

 the centre oblong-angular, arranged longitudinally, those 

 which form the bark, as it were, roundish and minute. 

 Fructification : — 1, pear-shaped spores, attached to threads 

 which radiate from a basal placenta, contained, within a 

 cellular pericarp, in ovate conceptacles ; 2, tripartite 

 tetraspores arranged irregularly in transverse bands below 

 the tips of the ultimate branchlets ; 3, antheridia collected 

 in terminal saucer-shaped receptacles. — Laueencia, named 

 in honour of M. de la Laurencie, a French naturalist. 



This genus contains several species, which are mostly 

 natives of temperate and tropical latitudes. Dr. Har- 

 vey, speaking of the American species, says that they 

 are very difiScult to determine, that "indeed in this 

 genus, as in many others, it is often impossible to tell 

 whether we are dealing with species or with sportive 

 forms, without a very careful examination of a number 

 of specimens, or without some knowledge of the cir- 

 cumstances accompanying their development." In a 

 modified degree this remark is applicable to our native 

 species, which, although abundant and well known, are 



