ALGAE 71 
A remarkable characteristic of the class is the absence 
of the motile reproductive cells so common in the brown 
and green alge. In the lowest members of the class, 
the Bangiacez, the reproductive cells are said to show 
a slight amceboid movement, but in all the others even 
such movement is quite wanting. Another peculiarity 
is the very evident protoplasmic connections between 
the cells of the thallus, these being constantly present 
in all but the lowest types. These connections have 
the form of extremely delicate filaments joining the 
protoplasmic bodies of adjacent cells (Fig. 19, A). 
They all possess in addition to the chlorophyll an 
additional pigment, which, in most forms, is a more or 
less pronounced red. This pigment (phycoerythrin) 
is least developed in the fresh-water species, which 
show a more or less decided green tinge, olive or black- 
ish rather than red. Many of the salt-water species, 
however, show a brilliant rose-red or purple color, to 
which they owe much of their beauty. This red pig- 
ment is soluble in fresh water and when it is extracted 
from the plants the chlorophyll-green becomes visible. 
The phycoerythrin seems to be related in its nature to 
chlorophyll, and probably is associated with it in the 
process of photo-synthesis. 
The red alge are small plants compared to the 
gigantic kelps, but are as a rule larger than the green 
alge. Some are exceedingly delicate, consisting of 
simple or branching filaments much like some of the 
Confervacee. Others are composed of single plates of 
cells, which form an excessively delicate, filmy thallus. 
Some, however, like the common Irish moss (Chondrus), 
and other species which grow where they are exposed 
