346 10 



it is only in slieltered places, however, that we meet with these algæ; on more 

 exposed places the bottom must be of a coarser consistency if the algæ are to be 

 able to fix themselves. We find therefore these algæ in shallow water in sheltered 

 localities and further in deeper water where the surf is not felt. Svedelius has 

 pointed out the same thing. 



(3| Rock and coral-reef Caulerpas. It is especially forms of Caiilerpa 

 racemosa we find here, but several of the above-mentioned Cati/erpa-species can also 

 be met with on a firm substratum. They can be divided into two groups, namely, 

 the forms which grow in exposed localities and those growing in sheltered ones. 



The first group is represented by Caulerpa racemosa f. rediicta which is found 

 in the most exposed places where Caulerpas are upon the whole found. It is only in 

 one locality that I have found it, namely, on the coral-reef to the west of Hurricane 

 Island which connects this island with St. Thomas. The locality is not completely 

 open to the ocean, in such quite exposed places we do not find any Caulerpas at 

 all and when Svedelius p. 87 writes that "C. lœtevirens f. laxa is a pronounced, 

 even though rare, example of a rock Caulerpa growing in strongly exposed localities 

 where no other alga happens to occur"'), this is in no way in accordance 

 with what is the case in the Danish West Indies, where indeed many algæ growing 

 in much more exposed places are to be found. The locality at St. Thomas men- 

 tioned here is somewhat sheltered by a small forelying island but nevertheless the 

 swell can run vigorously, especially through the sound east of Water Island, in 

 such a way that the waves break steadily on the reef. In this we find the forma 

 reducta growing in large patches, here and there mingled with other algæ e. g. 

 Cladophoropsis memhranacea, Diciifosphœria faviilosa, Valonias etc., all species of 

 algæ which form firm patches on which the sea breaks. If we consider a piece 

 of the Caa/erpa- patches, we find that it consists of a great quantity of rhizomes 

 entangled in each other to a firm tissue. By numerous richly ramified rhizoids 

 it is firmly fastened to the rocks. For more special description I may here refer 

 to the special part. 



Are we now going from these the most exposed places to more sheltered 

 ones, we find that the plants are larger in all regards. The rhizome is more 

 vigorous and well developed rhizoids attach the plant to the rocks and corals; 

 into the fine pores of the latter the rhizoids are easily able to penetrate. It is 

 especially the var. clavifera, uvifera and occidentalis we find here. 



What on the whole distinguishes the rock and coral-reef Caulerpa from the 

 sand Caulerpa is that the roots in the last mentioned first grow vigorously without 

 division some cms. down into the bottom and then suddenly become divided into 

 numerous rhizoids, whereas the roots of the rock and coral Caulerpa on the con- 

 trary are commonly directly divided into several branches, which by degrees are 

 divided into a great multitude of thin rhizoids. But on the other hand, an even 

 transition between the two forms is naturally to be found and as Svedelius has 

 ^J The emphasis is mine. 



