788 



ZONES AND REGIONS [Pt. Ill, Sect. V 



(Fig. 477, a), while small forms use correspondingly simpler devices — 

 gelatinous stalks in the case of Diatomaceae (Figs. 478, 479). The 

 number of species flourishing on muddy or sandy ground is small. Such 

 stations, at a greater depth or in agitated water, represent desert, in 

 which only stones, shells, and corals exhibit some vegetation, whereas 



jm 



Fig. 477. a Cladophora pygmaea, Reinke. Base with adhesive disk. Magnified 600. 

 b Ralfsia verrucosa, Aresch. Half natural size, c Chorda filum. Basal part. Natural size. 

 d Desmotrichum balticum, Kiitz., on Zostera. Natural size, e Microspongium gelatinosum, 

 Reinke, epiphytic on Fucus serratus. Natural size. 



in very calm and shallow bays they are usually occupied by swaying 

 meadow of sea-grasses. Only a few Algae thrive on sand or mud, for 

 instance species of Caulerpa and a few other Siphoneae, which are 



