THE MARINE BOTANIST. 143 



the shore ; when fresh it is of a reddish purple, or 

 salmon coloured; the root — if so it may be termed 

 — is a wide, flattened crust, from which spring 

 the articulated pinnate fronds. In the sub-order 

 of the Nulliporse, the fronds form lichen-hke 

 crusts on rocks, stones, &c., and on the stems of 

 algse ', and the fruit appears in little protuberances 

 on the surface. The dififerent species, or, perhaps 

 more correctly, varieties of form in this genus it 

 is not easy to separate from one another. Ac- 

 cording to Dr. Harvey, most of the thick, nulli- 

 porous crust found between tide-marks should be 

 referred to Melobesia polymorpha; and Dr. John- 

 ston considers all the species as only ill-developed 

 forms of Corallina officinalis. " It appears first," 

 he says, " in the guise of a thin, circular, calcareous 

 patch of a purpHsh colour, and in this state is 

 common on almost every object that grows be- 

 tween tide-marks. When developing on the leaves 

 of Zostera, or in other unfavourable sites, these 

 patches are usually pulvurulent and ill-coloured, 

 green or white, and never becoming large ; but 



