GROUP I- THALLOPHYTA : ALG^E. 221 



character, the presence (Algae) or absence (Fungi) of chlorophyll. 

 But the division is really natural, since this one character is 

 correlated with various others. It is, indeed, becoming usual to 

 regard the Algae and the Fungi as altogether distinct groups : but 

 it appears to be preferable to continue to regard them as classes of 

 the group Thallophyta, inasmuch as the Fungi have doubtless 

 arisen from the Algae, and since they possess many features in 

 common. 



CLASS I. 



These are plants of the simplest structure, which either live in 

 water in the form of green, blue-green, red, or brownish filaments 

 or masses of cells, or clothe damp surfaces such as rocks, walls, or 

 the bark of trees, with a covering of one or other of these colours. 

 In the sea they attain often a very considerable bulk ; some of 

 them are of a beautiful red or brown colour, and attract the 

 attention of the observer, partly by their considerable size, and 

 partly by the elegance of their form. 



The most important feature in which the plants of this Class 

 differ from the Fungi is the presence of chlorophyll and the con- 

 sequent mode of life. The Algae are able to form the organic sub- 

 stances necessary for their nutrition, whereas the Fungi are 

 obliged to obtain them from other organisms. The presence of 

 chlorophyll is obvious enough in the green Algae, but it exists also, 

 though less evidently, in Algae which have a bluish-green, olive- 

 green, brown, or red colouring-matter in addition in their chroma- 

 tophores. The nature of this additional colouring- matter is usually 

 the same throughout whole families which also resemble each 

 other in their modes of reproduction. Hence this characteristic 

 affords a trustworthy basis for classification, on which the Algae 

 are divided into the following sub-classes : 



Sub-class 1: CYANOPHYCEJ; (or Phycochromaceae), blue-green 



Algse, containing a blue colouring - matter 



phycocyanin ; 

 2 : CHLOROPHYCE^, green Algae, containing only 



chlorophyll and its derivatives ; 

 3 : PH^OPHYCEJ;, brown Algae, containing a yellow 



or brown colouring-matter phycophcein ; 

 4 : RIIODOPHYCEJ], red Algae, containing a red or 



purple colouring-matter phycoerythrin. 



