Mr. H. J. Carter on the Colouring Matter of the Red Sea. 1 87 



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 

 Euglence often become 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- 

 dinium above 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 Alga;, as in Spharoplea* and in 

 Protococcus pluvialis, where also in both it becomes green again 

 on germination, which led Colin to state that the green colour 

 is connected with " vegetation " or the early part of the existence 

 of the individual, and the red with ' c fructification " or the ter- 

 mination f. 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 Trichodesmium 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 com- 

 mon course, where Algse 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 unreasonable to infer that Tricho- 

 desmium Ehrenbergii does the same, and that, therefore, so 

 much of Montague's generic characters of Trichodesmium Ehren- 

 bergii 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 the same 

 organism in other parts of the world, one might cite those of 

 Peron, who likens it to "poussiere grisatre/' and of Darwin, 

 who compares it to "cut hay," &c. (op. cit.); but it seems better 

 for this argument not to go beyond the seas washing the shores 

 of Arabia. 



To what the "intense green," under which this organism 

 sometimes presents itself in the Red Sea, owes its production I 

 am ignorant, unless it be indicative of sporidification, which, 



* Cohn, Ann. des Sc. Nat. 4 e ser. t. v. p. 187. 

 t Ray Soc. Vol. for 1853, p. 519. 



13* 



