HOW TO KNOW THE SEAWEEDS 



9b Growth apical (terminal) or intercalary, but not trichothallic. Fig. 

 20 10 



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Fig. 20. An example of terminal growth 

 by means of an apical meristem in 

 which there is no evidence of a single 

 apical cell, as seen in a longitudinal 

 section of the apex of Gracilaiia. This 

 is sometimes called the "fountain 

 type" of apical meristem. 



Figure 20 



10a Thollus a simple, unbranched filament 250 /x in diameter or less, 

 with intercalary growth, at first uniseriate Fig. 21, later becoming 

 multiseriate Bangia 



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B 



Figure 21 



Fig. 21. Bangia fuscopurpurea (Dillwyn) Lyngbye 



A. A small portion of a young filament showing the uniseriate 

 character and flattened shape of the cells, X 190. B. An older part of 

 a filament showing the multiseriate condition, X 190. Growth is by in- 

 tercalary cell division. This dehcate but often abundant and conspicu- 

 ous plant occurs both on the Atlantic and Pacific coasts as a sHppery, 

 hairy covering on rocks and woodwork, the filaments sometimes reach- 

 ing 20 cm. in length. Several other minute epiphytic species of this 

 genus may be encountered. 



10b Thallus more than 500 a in diameter, branched or unbranched. .11 



32 



