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 Algze 
(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. 
