ALG^E 



67 



B 



with the other Algse. They include by far the largest 

 of the sea- weeds, and are familiar objects of the sea- 

 shore. With the exception of 

 a few forms like the gulf-weed 

 (Sargassum), which seems to be 

 really a floating plant, they are 

 usually firmly attached to rocks 

 and other objects by means of 

 highly developed root-like or- 

 gans or holdfasts. They may 

 grow where they are completely 

 submerged, but many of them 

 occur between tide-marks so 

 that they are partially or com- 

 pletely exposed at low tide. A 

 common feature of many of 

 them is the development of 

 floats, or air-bladders by which 

 the plant is buoyed up and 

 brought near the surface and 

 thus exposed to the light. 



Within this class there is 

 great range of structure as well 

 as size. The simplest forms are 

 delicate, branching filaments 

 much like many Confervacese, 

 except for their brown color. 



Others are gigantic plants reaching a length of a hun- 

 dred metres or more, rivalling the largest of terrestrial 

 plants. As might be expected, these giant kelps show 

 a considerable degree of specialization in their tissues, 

 but there is to be found almost every intermediate con- 



i. Ectocarpus 

 one of the 

 Brown Algae or Phreophycea ; 

 A, part of a plant showing 

 the sporangia, .sp; B, a uni- 

 locular sporangium, sp, more 

 highly magnified ; C, young; 

 D, older plurilocular spo- 

 rangium ; cl, the irregular 

 chromatophores ; E, a single 

 gamete of E. Siliculosus, 

 showing the lateral position 

 of the cilia. (Fig. E after 

 Berthold.) 



