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 Alge 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 
Pheophycee as well, true chromatophores occur, 
while they are absent, so far as is known, from the 
Cyanophycee. These chromatophores (chlorophores, 
erythrophores, pheeophores 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 Alge with the single known exception of 
Anthoceros (Hepatic). 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 Pheophycee, Rhodophycew, and Chlorophycew. 
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 
