184 CARTER, ON THE COLOURING MATTER OF THE RED SEA. 
Peridinium, by reflecting much more light than it did at first, 
comes rapidly into notice, and by its numbers gives a general 
red colour to that part of the sea in which it may be present. 
The same is frequently—indeed, commonly—the course with 
Euglena in fresh-water ponds. The little Protoceccus which 
colours the salt red in the salt-pans of the Island of Bombay, 
is green in the active period of its existence, but becomes 
red, and settles down into the “still form” of the same 
colour; while the common green Protococcus of the fresh- 
water tanks loses its red spot in the still form, and gains it 
again in the active or reproducing period of its existence. So 
red Kuglene often becomes green; but the usual course 
appears to be for the green to appear first. 
The red colour also appears to herald the termination of 
some period in the existence of the species. Thus the Peri- 
dintum ahove mentioned, after becoming red, loses its cilia, 
assumes the still form, and sinks to the bottom. The same 
is the case with the Protococcus of the salt-pans of Bombay ; 
but instead of adhering to the salt, it seeks out and settles 
upon the crystals of carbonate of lime that are among those 
of the salt. The chlorophyll changes from green to red also 
in some of the resting spores of the confervoid Algz, as in 
Spheroplea* and in Protococcus pluvialis, where also in both 
it becomes green again on germination, which led Cohn to 
state that the green colour is connected with ‘‘ vegetation ”’ 
or the early part of the existence of the individual, and the 
red with ‘‘fructification”? or the terminationy. So that, 
altogether, the passage of the colour from green to red in 
the filament seems to be more likely than the opposite. 
Thus, as the evidence regarding 7rochodesmium in the seas 
above mentioned is more, if anything, in favour of its yellow 
than its red colour, and that it is also sometimes green, while, 
in the common course, where algve present red and green 
colours in their respective cycles of existence, the latter 
appears first, and the Peridinium above mentioned passes 
from green to yellow and then to red, &c., it seems not un- 
reasonable to infer that Trichodesmium Ehrenberg ‘git does the 
same, and that, therefore, so much of Montagne’s generic 
characters of Trichodesmium Ehr enbergii as ‘relate to its 
colour (viz., that it is “at first red and at length green”) 
should be reversed. 
If it were desirable to adduce evidence of the faint green 
colour which Trichodesmium probably presents in the first 
stage of its existence, from the observation, too, of probably 
* Coln, ‘ Ann. des Se. Nat.,’ 4° sér., t. v, p. 187. 
7 Ray Soc. vol. for 1853, p. 519. 
