318 THALLOPHYTES 



a form with a small balloon-shaped plant body, which is commonly- 

 found projecting from moist soil, there are no sex organs and the 

 gametes are alike. 



The Siphonales are most peculiar in having a tube-like plant 

 body. In the production of well-defined sex organs they show 

 considerable advancement in sexual reproduction. 



Summary of Green Algae. — In having chloroplasts and well- 

 defined nucleus and cytoplasm, the cells of the Green Algae are 

 more advanced than those of the Blue-green Algae. In the 

 simplest forms the plant body is a single cell, either motile or 

 non-motile, and the uniting of cells into colonies is a prominent 

 feature. In the higher forms the plant body is multicellular and 

 in the form of a filament or disk. The multicellular forms have 

 not only established the habit of cells living together to form a 

 complex plant body but have also to some extent differentiated 

 cells. These habits look forward toward the formation of plants 

 consisting of a countless number of cells, which are differentiated 

 into tissues, such as occur in the higher plants. They introduced 

 sex cells which were at first alike, and later differentiated the sex 

 cells, thus introducing eggs and sperms, the sex cells of the higher 

 plants. They also introduced sex organs which are prominent 

 structures in the Mosses and Ferns. 



Brown Algae (Phaeophyceae) 



These Algae are marine forms, occurring on all sea coasts but 

 more abundantly in the cooler waters. They have two pigments, 

 chlorophyll and a brown pigment called fucoxanthin, but the 

 brown pigment obscures the green one and determines the color 

 of the plant. Both pigments probably help in the manufacture 

 of food, although the exact function of fucoxanthin is not known. 

 These Algae grow anchored by holdfasts to the rocks and their 

 bodies are so tough and leathery that they are not injured by the 

 beating of the waves. 



Although a few are simple filaments, most of them are much 

 more complex than any of the Green Algae. The plant body of 

 the majority of them not only consists of a greater number of 

 cells, but there is more differentiation among the cells than in the 

 Green Algae. In the largest of them the plant body often attains 

 a length of several hundred feet. As shown in Figure 274, the 



