THE RED ALGJE. 91 



the Silurian period, which have been preserved, can, it is 

 true, give us but a faint idea of them, because the material 

 of these Algfe, like that of most others, is ill-suited for pre- 

 servation in a fossil state. As has already been remarked, 

 a large portion of coal is perhaps composed of them. 



Less important is the fourth class of Algse, that of the 

 Rose-coloured Algce (Rhodophycese), or Red Sea-weeds (Flc- 

 ridese). This class, it is true, presents a great number 

 of different forms ; "but most of them are of much smaller 

 size than the Brown Algae. Although they are inferior to 

 the latter in perfection and differentiation, they far surpass 

 them in some other respects. To them belong the most beau- 

 tiful and elegant of aU Algae, which on account of the fine 

 plumose division of their leaf -like bodies, and also on account 

 of their pure and delicate red colour, are among the most 

 charming of plants. The characteristic red colour some- 

 times appears as a deep purple, sometimes as a glowing 

 scarlet, sometimes as a delicate rose tint, and may verge 

 into violet and bluish purple, or on the other hand into 

 brown and green tints of marvellous splendour. Whoever 

 has visited one of our sea-coast watering places, must have 

 admired the lovely forms of the Florideae, which are fre- 

 quently dried on white paper and offered for sale. 



Most of the Red Algge are so delicate, that they are quite 

 incapable of being petrified ; this is the case with the splendid 

 Ptilotes, Plocamia, Delesseria, etc. However, there are in- 

 dividual forms, like the Chondria and Sphaerococca, which 

 possess a harder thallus, often almost as hard as cartilage, 

 and of these fossil remains have been pj-eserved — principally 

 in the Silurian, Devonian, and Carboniferous strata, and 

 later in the oolites. It is probable that this class also had 



