487 



purpose of studying the algal vegetation, as during my earlier 

 visits I had mostly been occupied with the flora, but the out- 

 break of the war suddenly put an end to my preparations for 

 the journey. 



When an algologist who is only familiar with the algal vege- 

 tation of our Northern seas - - dependent upon a rocky coast or 

 other firm substratum for its existence - - for the first time comes 

 in contact with the tropical algal vegetation, he cannot fail to be 

 immensely struck with the extraordinary richness and variety 

 of form of the tropical algal flora which flourishes on a loose and 

 yielding sea-bottom and is formed of types which are altogether 

 absent from the Northern seas. I briefly dealt with this matter 

 for the first time in 1898 in the book written by Prof. OVE PAUL- 

 SEN and myself (Om Vegetationen paa de dansk-vestindiske 0er, 

 Ivj0benhavn 1898, p. 4; also in Botan. Tidsskr. Vol. 22). Since 

 then I have gone into the matter in more detail in later papers 1 ) 

 and therefore I shall not deal further with it here. 



Another really just as strange occurrence of alga? in the 

 West Indies is the vegetation which is fastened to the roots of 

 the mangrove (Rhizophora mangle). The algse find the rather un- 

 even surface of the roots a favourable place to fasten themselves, 

 and the fact that the water can circulate freely round the roots 

 also contributes to favour this habitat. Consequently the result 

 is that those mangrove roots which grow in the water, where it 

 is salt and not stagnant, are overgrown by a vigorous and often 

 very luxuriant algal vegetation. I have also mentioned this in- 

 teresting vegetation in an earlier paper, namely in the above 

 quoted volume published on the occasion of Professor WARMING'S 

 seventieth birthday. 



Upon the coral reefs and upon the larger and smaller blocks 

 broken off from these we find near the surface of the sea and in 

 shallow water several Caulerpa-iorms covering the blocks and 



l ) B0RGESEN, F., A contribution to the knowledge of the marine Alga 

 vegetation on the coasts of the Danish West-Indian Islands (Bot. Tids- 

 skrift, vol. 23, 1900). An ecological and systematic account of the Cau- 

 lerpas of the Danish West Indies (Kgl. danske Vidensk. Selsk. Skrifter, 7. 

 Raekke, Naturv.-mathem. Afd. IV, 5, 1907). The algal vegetation of the 

 lagoons in the Danish West Indies. (Biologiske Arbejder tilegnede EM.. 

 WARMING, den 3. Nov. 1911, Kobenhavn). 



