THE VARIETY OF PLANT LIFE 



87 



The remainder of the thallus plants include some phyla with 

 chlorophyll-bearing species and others which lack the chloro- 

 phyll. All have a more complex cell structure and body organiza- 

 tion than the Schizophyta. The green thallus phyla are almost 

 entirely restricted to aquatic habitats, being unable to survive 

 dessication resulting from living beyond the reach of spray or 

 high tides. These phyla form the variety of pond scums and 

 blooms which appear in streams and ponds, as well as the 

 numerous seaweeds which colonize the oceans. Many are micro- 

 scopic and unicellular; a few are massive and resemble land plants 



Fig. 56. — Blue green algae are slimy water plants closely related to the bacteria. 



in form and size; but the majority are delicate individuals built 

 up on the filamentous body plan. The distinction between the 

 various phyla of these green Thallophytes is based upon the pres- 

 ence or absence of auxiliary pigments which often obscure the 

 chlorophyll. In the Chlorophyta the green color is very evident, 

 the chlorophyll being associated with no other pigment; these 

 plants are therefore known as the Green Algae. A brown pigment, 

 fuco-xanthin, gives an olive-brown or black tinge to the plants 

 of the Phaeophyta, which are appropriately known as the 

 Brown Algae. And the red pigment, phycoerythrin, found in the 

 Rhodophyta often obscures the chlorophyll to such an extent 

 that the plants appear rose-red or purple in color, and are called 

 the Red Algae. 



