88 PLANTS AND MAN 



The phylum Chlorophyta or Green Algae, occurs in both 

 fresh and salt water, comprising some 5000 species. Many of the 

 fresh water forms are filamentous like Ulothrix and Spirogyra while 

 others are unicellular as are the desmids (see p. 24). In the 

 oceans the Green Algae are those seaweeds which grow around 

 high tide mark; some are filamentous and mossy in appearance 

 while others form expanded blades which float like torn leaves in 



Fig. 57. — Green algae are common seaweeds about high tide mark; some are 

 hair-like and mossy, others form thin sheets. 



quiet harbors (fig. 57). Green Algae are of little economic impor- 

 tance except as food for fishes and other aquatic animals. 



There are less than 1000 species in the phylum Phaeophyta 

 or Brown Algae, which however are the dominant plants in the 

 region from low tide mark to depths of fifty and sixty feet. Those 

 that inhabit the rocks around low tide mark include the slippery 

 olive-brown seaweeds familiar to every one who has prowled 

 along rocky shores: of these the common rockweed or bladder- 

 wrack with its swollen bladders is typical. Others have a habit 



