206 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 Rhodophycew are classified under four orders, 
viz., the Nemalionacece, the Gigartinacew, the Rhody- 
meniacece, and the Cryptoneniacew, according to the 
Fic. 61.—Tetraspores. a, tetrad (Callithamnion); b, cruciate (Gracilaria) ; 
c, zonate (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. 
