26 SEAWEEDS 



forms if anything, fresh-waters are richer in such 

 types, while on the other hand the sea is incompar- 

 ably more favourable to diversity of vegetative 

 development and to luxuriance of habit as well. 



It was at one time supposed that among the red 

 and green Algae there were forms in which the 

 chlorophyll was diffused throughout the protoplasmic 

 cell-contents, but research has shown that in all 

 cases examined in these groups and in the 

 Phwophycece as well, true chromatophores occur, 

 while they are absent, so far as is known, from the 

 Cyanophycecc. These chromatophores (chlorophores, 

 erythrophores, phoeophores or melanophores, as the 

 case may be) sometimes contain pyrenoids minute 

 bodies (appearing within them much as a nucleolus 

 appears within a nucleus) confined to the chromato- 

 phores of Algae with the single known exception of 

 Anthoceros (Hepaticae). The chromatophores occur 

 either singly in each cell or in numbers, and are 

 of definite and characteristic shapes. These shapes 

 are not only of constant character, but the same 

 constancy extends to the fact of their single or 

 numerous occurrence in each cell. The presence or 

 absence of pyrenoids, which may vary in size from 

 time to time, affords a more capricious character, 

 since forms possessing them are found among 

 the PhceopJiycece, Rhodophycece, and Chlm^opliycew. 

 Various attempts have been made to attach special 

 significance to the occurrence of pyrenoids, but so 

 far there has not been much success in elucidating 

 this point. There is, for example, no clear ground 

 for the view that their presence is connected with 



