INTRODUCTION TO CRYPTOGAMIC BOTANY. 197 



in the open sea, are sufficiently abundant. Mduhcs'ia occurs as 

 high as T-t" N. lat; there are, however, many genera which affect 

 warmer seas, especially those of Australia, and they abound in 

 the tropics. Gorallina offiycinalis, as its name implies, is ad- 

 mitted into the Pharmacopeia on account of its calcareous 

 nature, but there is no peculiar virtue in it which makes it 

 superior to other similar chemical matters. Dr. Johnston be- 

 lieved the Melobesue to be mere states of Corallina qfficinalis. 



IT-i. I am not aware whether corallines are grazed upon 

 by fish, as coral is by the genus Sparus. Mr. Darwin has de- 

 .scribed the manner in which chalk is formed in the latter case, 

 and, from the large quantity of carbonate of lime which these 

 plants contain, it is highly probable that they contribute their 

 share to its formation.* 



13. Laurenciace^, Harv. 



Cylindrical or compressed, cartilaginous. Conceptacles ovate, 

 with a terminal pore. Spores pear-shaped, radiating from a 

 basal placenta. Tetraspores lodged in the branchlets. 



175. These agree with the next tribe, Rhodomelacece, in 

 fruit ; but the frond in the greater number of species is inarti- 

 culate and solid, though sometimes tubular and septate, with the 

 superficial cells minute, and not forming evident reticulations ; 

 the tetraspores too are scattered over the branchlets. The 

 antheridia are highly developed, and assume curious forms, 

 in those cases where they have been observed. Nothing can 

 be more variable than the colour, even in the same species. 

 Laurencia affords some of our commonest Algae, and it is well 

 known to every collector how these vary. When perfect they 

 are of a dull purple or brownish red ; but these tints pass 

 through every shade to orange, and yellow, and green, 

 according to the degree of their exposiu-e, in shallow pools, 

 or open rocks, to the action of light and air, while fresh 

 water is rapidly destructive. Others, like Asparagopsis, are 

 of a beautiful pink ; while Charnpia assumes the hues of 

 Polysiphonia, exhibiting, like many other Algae, prismatic 

 colours. The species are very widely distributed, occurring in 

 very different localities. Champia, as originally understood, 

 * Darwin, Journal, p. 553. 



