186 Dansk Botanisk Arkiv, Bd. 3. Nr. 1. 



The specimens found seem to agree very well with the de- 

 scription given by M™*^ Weber and quoted above. The most 

 characteristic feature of this species is that the long cylindrical 

 joints are swollen padhke at both ends in the older parts of the 

 thallus (comp, the fig. b of Kützing, 1. c). 



As pointed out by M^^^ Weber the central strand consists of 

 a variable number of rows of long cells, interrupted by one or 

 two rows of short cells. In the specimens examined by me I 

 have found 4 — 6 rows of long cells, their length varying from 

 about 55 — 90//, that of the short ones from 15 to 30;/. 



The nodes have nearly the same anatomical structure as 

 that found in the joints, only that the walls of the cells are 

 somewhat thicker and not calcified. M=^^ Weber has given a 

 very fine illustration of the node (1. c). 



The conceptacles form small, roundish, prominent cushions 

 along the sides of the joints. I have only found tetrasporic plants. 

 The tetrasporangia are about 50 /r/ long and 25// broad and often 

 taper upwards in such a way that the uppermost spore has a 

 conical shape. 



Having examined the authentic specimens of Amphiroa ciispi- 

 data and A. cyathifera and having found that their anatomical 

 structure does not differ from that of Am. fragilissima M™^ Weber 

 comes to the conclusion that these two species are only forms of 

 the present plant. When stating this M"^*^ Weber adds : "I do 

 not attach great importance to this point, whether specimens are 

 more or less slender, if they agree on all other points". I share 

 this view with M™^ Weber especially as my plants differ much in 

 this respect the varying strength of the plants seeming to originate 

 from the locality in which the plants are found. This is easily 

 illustrated by an example. Specimens found near Cruz Bay, St. 

 Jan, growing in an exposed place where the waves constantly 

 dashed the plants, form very compact, dense tufts ; they have 

 comparatively short and thick joints, the diameter of which in 

 the middle of the thallus reaches a length of about 460//. On 

 the other hand specimens from sheltered localities and those 

 growing between and protected by sea-grasses are more slender, 

 forming loose and open tufts, with much longer and thinner joints, 

 their diameter reaching only a length of about 190/^. 



This species is very common along the shores of the islands 

 and occurs both in sheltered and exposed localities, in shallow 

 water and in deep sea down to a depth of 10 fathoms or even 

 more. It often grows abundantly upon coral reefs and here, 



