THALLOPHYTES 



17 



the rest in size and form and contents, and serves as a hold- 

 fast for anchoring the plant. This anchoring cell is found 

 in a great many filamentous forms, and 

 shows that differentiation of form, etc., 

 has to do with difference of work. Among 

 the marine Alga3 this differentiation be- 

 comes very great. For example, in such 

 seaweeds as are illustrated in Figs. 9 to 

 14, there are complex holdfasts (often 

 looking like roots), stalks (resembling 

 stems), and leaf-like portions (which 

 may just as well be called leaves). In 

 these cases, not only is the body differ- 

 entiated into dif- 

 ferent regions, but 

 the cells composing 

 each region are dif- 

 ferentiated. 



To summarize 

 these statements in 



reference to the vegetative bodies of 

 AlgaB, it may be said that the Algae 

 begin as one-celled plants and become 

 many-celled plants ; that the cells of 

 the many-celled forms become differ- 

 entiated ; and that finally the many- 

 celled body becomes differentiated 

 into different regions. 



13. Reproduction. The preceding 

 sections give an account of the vege- 

 tative body of Algae. It now remains 

 to consider the methods of reproduc- 

 tion developed by the Alga?. It must 

 be understood that reproduction began as a relatively simple 

 process, and that it became gradually more and more com- 



FIG. 11. Nereocystis : 

 a bladder kelp, show- 

 ing the blades arising 

 from the bladder-like 

 expansion of the end 

 of the stalk. 



FIG. 12. Fucus: fragment 

 of rockweed, showing the 

 forked branching, the 

 swollen tips in which the 

 sex-organs are produced, 

 and the air bladders (three 

 of them near the base). 



