REPRODUCTION OF SEA-WEEDS. 3 



is so variable or uncertain as colour. Far from serving 

 as a mark to distinguish groupes, or genera, the utmost 

 to which it can pretend is to separate one variety of 

 species from, another. 



" Among Algae, on the contrary, it has been ascer- 

 tained that the classes of colour enumerated before, 

 are, to a great extent, indicative of structure, and of 

 natural affinity. Thus, the green species are of the 

 simplest structure, and differ remarkably in their mode 

 of reproduction from either of the other tribes : — their 

 seeds being endowed at the germination with a sort of 

 motion which some have called voluntary, but which 

 really does not possess that animal property. 



" The olivaceous (Melanospermeae) are the most per- 

 fect and compound, and reach the largest size. The 

 red series (Ehodospermese) form a group not less dis- 

 tinguished by the beauty and delicacy of their tissue, 

 than by producing seeds under two forms ; — thus 

 possessing what is called a double fructification." 



Most Algae are, at some period of their growth, found 

 attached to other substances, by means of a root, or, at 

 least, a hold-fast. It has been doubted whether, as no 

 distinct vessels of absorption have been discovered, they 

 receive any nourishment through this organ ; but the 

 question is by no means settled.* Thus much is, at 



* From attentive observation, during the last four or five 

 years, I have myself come to the conclusion that marine 



b 2 



