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SEAWEEDS 



branches called stichidia. This is the most common 

 form of reproduction, and usually occurs in a succes- 

 sion of generations, while the plants bearing the 

 sexual organs occur for the most part only at 

 particular seasons. 



The Rhodophycecc are classified under four orders, 

 viz., the Nemalionacecc, the Gigartinacece, the Rhody- 

 meniacece, and the Cryptonemiacem, according to the 



FIG. 61. Tetraspores. a. tetrad (Callithamnion) ; b, cruciate (Gracilaria) ; 

 c, zonatc (Catenella). Highly magnified. 



four main types of development of the carpogonium, 

 and these orders are subdivided into families based 

 on characters derived from the gonimoblasts and the 

 whole cystocarp fruits. Since, as has been said, 

 there is no constant correspondence of vegetative 

 characters with reproductive characters, it is not 

 possible to describe the former as distinctive of orders 

 or families, but the prevailing kind of thallus will 

 be indicated under each family. 



