342 6 



that often to such a degree that it is impossible to see the bottom even in quite 

 shallow water. The bottom is soft and consists of grayish mud mixed more or 

 less with sand. By reason of the muddy water the light is moderate and the 

 mangroves also, where they occur, cast a rather strong shadow, which is of special 

 importance for the Caulerpas growing on the roots. Finally it must be pointed out 

 that the water after heavy rains may become very brackish. 



The conditions of life which the algæ meet with here are therefore, firstly 

 shelter, further moderate light, slight renewal of the water which probably is often 

 very brackish ; finally an often very soft bottom. 



In spite of these, one would think anything but favourable, conditions of life 

 we find in the lagoons an often very rich alga-vegetation covering quite densely the 

 soft bottom. Penicillus capitatus is especially caracteristic for these localities but 

 among them creep several CaH/er/ja-species often in great number (cfr. Borgesen 

 7, p. 4 and 5, p. 51 — 54). 



Finally, we find the Caulerpas in deeper water out in the more open sea. 

 The conditions of life which are offered the algæ here are, firstly, quiet at least 

 from the movement of the sea owing to the greater depth; on the other hand a 

 relatively strong current may probably often occur here and the water is therefore 

 constantlj' renewed; further, the light is moderate; compared with those in shallow 

 water the conditions of life, e. g. the temperature, salinity etc. in deeper water, may 

 on the whole be characterized as very uniform. 



Naturally these mutually so different localities are, as I have already pointed 

 out, connected by imperceptible transitions. The sheltering coral-reef need only be 

 a little higher for example, so that the waves more rarely wash over it, and the 

 water behind will then only more seldom be renewed, the bottom will be softer, 

 the finer particles being able to precipitate, and we thus get an imperceptible 

 transition to the stagnant water in the lagoon, quite in the same way as we have 

 from shallow water an imperceptible transition to the deeper. I have chosen these 

 different types of localities, not only because it seems to me that these can be 

 considered as the chief types about which the others can be arranged, but also 

 because we just here find characteristic forms of the algæ. 



In these different localities we now find the Caulerpas, which is in good 

 accordance with what Svedelius has observed in Ceylon and quite in contradiction 

 to the view of Reinke (27) concerning the occurrence of the Caulerpas (about which 

 more later on). 



When SvEDEHus (30, pag. 82) however writes : "Concerning the ecology of the 

 Caulerpas, there are in the botanical literature very few, indeed practically no 

 reports" I can, however, not quite agree with him, even if it is quite true for the 

 most part that we only find but little. I shall not here mention in more detail 

 my little preliminary paper (5) on the algal vegetation in the Danish West Indies 

 which has hitherto been unnoticed') but in which, however, somewhat is said 

 ') e. g. also in Oltmann's Morphologie und Biologie der Algen. 



