180 CARTER, ON THE COLOURING MATTER OF THE RED SEA. 
But to Ehrenberg is due the merit of having first described 
(in 1826) the nature of the organism from which this 
colouring matter is derived. He found it in the Bay of Tor 
itself, pronounced it to be an Oscillatoria, and called it Tri- 
chodesmiun erythreum,which Montagne has advisedly changed 
to T. Ehrenbergi. 
No one who has read Montagne’s memoir, and seen his 
illustration together with the organism itself, can doubt that 
the chief source of the red colour of the Red Sea is owing 
to the presence of this little Oscillatoria. Nor can any one 
doubt, who has read M. Dareste’s memoir, that this is not 
the only organism which colours the sea red in different parts 
of the world. 
It was to confirm the observations of the latter, as well as 
to record the fact itself, that I wrote the paper in these ‘Annals’ 
for 1858 (vol. i, p. 258), entitled ‘On the Red Colouring 
Matter of the Sea on the Shores of the Island‘of Bombay,” 
wherein it is shown that this colour depends on the presence 
of a Peridinium (P. sanguineum, Cart.) in innumerable 
quantities, in which the chlorophyll at first is green, then 
becomes yellow, and lastly red, when the latter, mixing with 
the oil-globules generated pari passu in the cell, gives rise 
together to greater opacity, and thus reflecting more strongly, 
makes the presence of the Peridinia more evident, and causes 
the sea in which they are contained rapidly and almost 
suddenly to become of a vermilion or minium-red colour ; 
after which, the Peridinium falls to the bottom and thus 
disappears, as if this were the termination of a cycle in its 
existence. 
It was not, however (although I had formerly spent many 
months on the coasts of Arabia), until returning to England 
in June, 1862, on board the Peninsular and Oriental Company’s 
steamer ‘Malta,’ that I had an opportunity of seeing the colour 
of the Red Sea which is produced by Trichodesmium Ehren- 
bergii—a circumstance to which I should not have alluded 
had not Montagne appended to his memoir certain queries 
which, in part, I can answer, at the same time that, with much 
diffidence, I offer a few remarks on Montagne’s generic cha- 
racters of this organism, which are repeated by Kiitzing in 
his ‘Species Algarum.’ 
Commencing, then, with a short account of my own ex- 
perience of Trichodesmium Ehrenbergit in the Red Sea, I 
would observe that, on the 31st of May, 1862, when approach. 
ing Aden, we passed through large areas of a yellowish-brown, 
oily-looking scum on the surface of the sea, and that on the 
2nd of June, when off the Arabian side of the first islands 
