DEVELOPMENT OF PLANTS 



185 



(b) The Coarser Brozvn Algae, the Kelps. This latter condi- 

 tion is well illustrated in the kelps, plants related to Ectocarpus, 

 which include the largest and most highly organized forms of 

 all the algae. Indeed some of these forms are quite comparable 

 in size with our shrubs and trees. The Laminarias (Fig. 120, A) 

 of our Atlantic coast have stalked blades ten to twenty feet long. 

 The great bladder kelps of the Pacific, Nereocystis and Macro- 

 cystis, attain great dimensions, the latter genus reaching a length 

 of 500 to 900 feet and Lessonia with trunk-like stems and leaf- 

 like segments forms veritable submerged forests in the Ant- 

 arctic Ocean (Fig. 120, B, C). These highly organized plants 

 have apparently lost or failed to develop a sexual method of 

 reproduction and depend entirely upon the formation of zoo- 

 spores for their propagation. 





FIG. 121. Two common forms of the Fucaceae: A, Sargassum, the 

 stem-like axis bearing air sacs, s, and leaf-like organs; g, reproductive 

 branches. B, Fucus s, air sacs; g, reproductive branch. C, young plant. 



The rock weed or bladder wrack (Fucus) and the gulf 

 weed (Sargassum) are representatives of a group, Fucaceae, 

 that contain the most specialized of the brown algae (Fig. 121). 



