CONTINUED: CLASSIFICATION. 



i6 7 



with new valves. The valves are often marked with numerous and fine 

 lines, often making beautiful figures, and some are used for test objects for 

 microscopes. 



The free forms are capable of movement. The movement takes place in 

 the longitudinal direction of the valves. They glide for some time in one 

 direction, and then stop and move back again. It is not a difficult thing to 

 mount them in fresh water and observe this movement. 



The diatoms have small chlorophyll plates, but the green color is dis- 

 guised by a brownish pigment called diatomin. The relationships of the 

 diatoms are uncertain, but some, because of the color, think they are re- 

 lated to the Phaeophyceae. 



Class Phaeophyceae. 



369. The brown algae. (Phaeophyceae). The members of this class pos- 

 sess chlorophyll, but it is obscured by a brown pig- 

 ment. The plants are accessible at the seashore, 

 and for inland laboratories may be preserved in 

 formalin (2\ per cent). (See also Chapter LVI.) 



360. Ectocarpus. The genus Ectocarpus repre- 

 sents well some of the simpler forms of the brown 

 algae (fig. 172). They are slender, filamentous 

 branched algae growing in tufts, either epiphytic on 

 other marine algae (often on Fucaceae), or on stones. 

 The slender threads are o:Jy divided crosswise, 

 and thus consist of long series of short cells. The 

 sporangia are usually plurilocular (sometimes uni- 







Fig. 172. 



A Ectocarpus siliculosus; B, branch with a young and a ripe 

 plurilocular sporangium; E, gametes fusing to form zygospore. 

 (B, after Thuret; E, after Berthold.) 



