Xviii INTRODUCTION. 



D. aculeata, says, that these species remain unaltered 

 while they cause decay around them. But this I have not 

 found to be the case. The Desmarestia always loses its 

 rigidity, and its original olive is changed to verdigris before 

 it possesses any destructive power. The Fucoidecs become 

 black on exposure to the air. The Laminaria, on the 

 contrary, first become green and finally white, under simi- 

 lar circumstances. Many of the Floridete are much bright- 

 ened in colour after having been cast upon the beach, 

 especially if exposed to rain and sunshine. Amongst those 

 of our own shores, Plocamium coccineum and Dasya ooc- 

 cinea are conspicuous in this respect. Both are, originally, 

 of a dull, deep pink, but when thrown up and a short time 

 exposed, become of a veiy rich scarlet-crimson. But Ge- 

 lidium cartilagineum, so common at the Cape of Good 

 Hope, often presents the most splendid gradation of colour 

 in a single specimen, from dull purplish pink (its original 

 dye) through scarlet, orange, yellow, and verdigris-green 

 to white ; to which colour all the red and green species 

 may be bleached after long exposure. 



Among the more delicate tribes several are instantly al- 

 tered by being plunged into fresh water. Nitophyllum 

 versicolor, as Mrs. Griffiths has observed, is remarkable in 

 this respect; its full pink being instantly changed to a 

 bright orange. Delesseria hypoglossum and ruscifolia have 

 the same peculiarity, as have many of the Callithamnia 

 and Griffithsia, and other delicate Rhodosperms. All these 

 changes are accompanied by decomposition. In the case 

 of Griffithsicn* especially, shortly after the change, the co- 

 louring matter of the joints is abundantly discharged with 

 a crackling noise through the ruptured membrane, staining 

 with a beautiful carmine colour the water or the paper to 



* See an excellent description of this in a paper by Dr. Drummond, 

 of Belfast, in ' Mag. Nat. Hist.' vol. ii. p. 121. 



