Indian Ocean, and the Cape of Good Hope. 69 



from the Orinoco floods a condition that would operate in the same 

 direction.' We can now check this speculation by a comparison with 

 the figures for the Indian Ocean, mainly derived from such localities as 

 the Red Sea, Ceylon, Mauritius, &c., in no case affected by the question 

 of fresh-water floods. The figures for the Indian Ocean are very nearly 

 the same for both groups 24 genera and 117 species of PJiceopJiycece, and 

 26 genera and 121 species of Chlorophycea thus showing indirectly that 

 the irruptions of fresh water are, in all probability, potent in the case 

 of the West Indian Algae. One is much struck by the strength of 

 illumination of the bottom in a shallow coral sea, but the filtering action 

 by sea water of the rays of light, and the interception first of those 

 rays that are most efficient in the work of assimilation conditions 

 modifying the pigments of Algae are the same in all seas.* The 

 practically tideless character of the Antilles would also make for a 

 preponderance of green over olive-brown forms. 



GEORGE MURRAY. 



* Recent research on other pigments by Prof. Marshall Ward makes it appear to 

 me more probable that, in the case of the marine Algae, the pigments are rather shields 

 against the excess of blue rays than adaptations to heighten the succeptibility of 

 chlorophyll to the diminished supply of the others. 



K 



