182 SEAWEEDS 



stage, and their reproduction is always by mere cell- 

 division. The reported conjugation may be regarded 

 as extremely doubtful. 



The Thallus. The membrane consists of' a sub- 

 stance nearly related to cellulose, sometimes impreg- 

 nated with carbonate of lime (though this is not the 

 case in Ceratium), and its growth has been described 

 as peculiar, and not to be adequately explained by 

 apposition or intussusception. In the marine forms, 

 at all events, the protoplasm consists of two zones, 

 the outer one being hyaline towards the outside and 

 granular towards the inside. In this granular por- 

 tion are embedded the chromatophores and fatty 

 drops and plates. The interior body of protoplasm 

 is very finely granular, and contains the nucleus and 

 vacuoles. The chromatophores support three dif- 

 ferent substances, viz. phycopyrine, peridinine, and 

 chlorophyll. 



In some of the fresh- water forms an animal-like 

 nutrition has been described, and green Algae 

 (Chlamydomonas and others) are stated to have been 

 ingested and partly digested. In such forms no 

 chromatophores occur, and the starch present must be 

 the fruit of such captures. It is apparent from such 

 observations, and from others, that very diverse organ- 

 isms have been gathered together under this order. 



Reproduction is always by division, and since it 

 appears to occur in the most varied way among the 

 fresh-water forms in some cases during the motile 

 phase, in others during the resting stage and after 

 encystment this fact lends support to the view that 

 the order is not very coherent. 



