F. Borgesen : Rhodophyceæ of the Danish W. Indies. 245 



Falkenberg, who also points out the difficulties encountered 

 in attempting a definition of the species, in his very valuable 

 work on the Rhodomelaceae, p. 252, gives some starting points 

 from which to proceed to the said definition of the species. 



As a chief characfteristic he places the radial type opposite 

 to the flat, bilateral. He further quotes the more or less vigorous 

 ramification, especially if the latter is alternate, or shows a more 

 or less marked tendency to become opposite or verticillate. As 

 an example of a species with alternate branching he names 

 L. papulosa, as one with verticillate branching L. obtiisa. Further- 

 more be mentions as a subcharacteristic the more or less vigorous 

 development of the side-branches, these in some species forming 

 long filaments like the main filament, in others short wart-like 

 ones. 



Falkenberg also mentions (1. c, p. 246) the ditYerent struc- 

 ture of the antheridial stands, as found in Laurencia obtusa and 

 pinnatifida, and points out that such differences are perhaps to be 

 found, too, in other species. Unfortunately the antheridial stands 

 are as yet unknown in most of the species. 



1. Laurencia Poitei (Lamour.) Howe. 



Howe, M. A., Phycological studies, II, in Bull. Torr. Bot. Club, vol. 

 32, 1905, p. 583. 



Fucus Poitei Lamour., Dissertations sur plus, especes de Fucus, Agen 

 1805, p. 63, tab. 31, figs. 2—3. 



Laurencia gemmifera Harv., Nereis Bor.-Am,, part II, 1852, p. 73, tab. 

 18 B. 



Laurencia tuberculosa J. Ag., Spec. Alg., vol. II, p. Ill, 1863, p. 760. 



Laurencia mexicana Kiitz., Tab. Phycolog., vol. XV, 1865, p. 25, tab. 

 70, figs, c, d. 



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

 scriptions and figures of Harvey. It is a relatively large plant, 

 often reaching a length of 15 cm or more. The thallus is rather 

 robust and cartilaginous. 



Upon a transverse section the central axis is not very visible, 

 the tissue consisting in the middle of larger, towards the peri- 

 phery of smaller, roundish cells. The peripheric cells are rather 

 small, in transverse section nearly subquadratic. While most of 

 the specimens had a glabrous surface, some specimens (my collec- 

 tions no. 1504) had the peripheric cells provided with small pa- 

 pillae (Fig. 235). They were present in the young parts of the 

 thallus, in older parts they seem to disappear. I cannot say 



