238 PART IV. CLASSIFICATION. 



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 siib- 

 stances necessary for their nutrition, whereas the Fungi are obliged 

 to obtain them from other organisms (p. 195). 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 : CYANOPHYCEJS (or Phycochromaceae), blue-green 

 Algae, containing a blue colouring -matter 

 phycocyanin ; 

 ., 2 : CHLOROPHYCEJE, green Algae, containing only 



chlorophyll and its derivatives ; 

 3 : PELEOPHYCE.E, brown Algae, containing a yellow 



or brown colouring-matter phycophcein ; 

 4 : RHODOPHYCE.E, red Algae, containing a red or 

 purple colouring-matter phyc.oerythrin. 



The colouring-matters phycocyanin, phycophsein, and phycoerythrin, 

 can be extracted by means of water; they thus differ from chlorophyll, 

 which is insoluble in water. The presence of chlorophyll in the 

 Cyanophyceae, Phaeophycese, and Rhodophyceae, can be proved by ex- 

 tracting the other colouring-matters with water ; the plants then assume 

 a green colour. 



Structure. The body may be unicellular ; or coenocytic and 

 unseptate (as in the Siphonaceae), or incompletely septate (Clado- 

 phoraceae) ; or multicellular. The unicellular forms either exist 

 singly, or a number may be held together in a colony by a mucila- 

 ginous common cell- wall, either as a filament (e.g. some Desmidiese) 

 or a mass (palmelloid Protococcaceae, Chroococcaceae). In some of 

 the multicellular forms (e.g. Spirogyra, Pandorina, Ulva) all the 

 cells of the body are quite similar; at first vegetative, they 

 eventually become reproductive, so that there is no distinction 

 between nutritive and reproductive cells: in these histologically 



