F Børgesen: Rhodophyceæ of the Danish W. Indies. 



247 



Fig. 235. Laurencia Poitei 

 (Lamour.) Howe. Transverse sec- 

 tion of the peripheric tissue of 



the thallus. (About 150:1). 



a few cm in height, in somewhat more 

 sheltered places it grows higher, up 

 to 10 cm or even more. 



It is firmly fastened to the 

 rocks by means of a broad and 

 rather thick disc, from which several, 

 and often many, erect branches 

 grow up. 



Growing as it often does in the 

 most exposed places, the thallus is 

 of a very firm and cartilaginous con- 

 sistency. The tissue of the plant is also built quite according to 

 its habitat. The epidermal cells, when seen from above, are small, 

 roundish and have very thick walls; upon a transverse section 

 they are found to be long and narrow like palissade cells (Fig. 236). 

 They are about 25 /i long and 8;/ broad. Also the cells in the 



interior of the thallus have thick walls. The 



central cylinder is not easily distinguishable. 

 Only plants with tetraspores were found. 

 These are formed in the summit of the wart- 

 like ramuli. 



It is a common plant along the more open 

 Fig. 236. Laurenciapa- parts of the coast of the islands. 

 pillosa (Forsk.) Grev Geogr. Distrib.: Warmer parts of the At- 



1 rcinsv6rs6 S6Ction oi nr t n t^jo c* a 



peripheric part of lantic Ocean, Mediterranean Sea, Ked bea, bana- 



thallus. (About 200:1V wich Islands etc. 



mwm 



3. Laurencia obtusa (Huds.) Lamour. 



Lamouroux, J. V. F., Essai in Annales du Museum d'Hist. Nat., vol. 

 20, 1813, p. 130. J. Agardh, Spec. Alg., vol. II, p. 3, p. 750; Epicrisis, p. 653. 

 Harvey. Phycologia Brit., pi. 148. 



Fucus obtusus Huds. Fl. Angl., p. 586. Turner, D., Fuci, vol. I, tab. 21. 



The specimens I refer to this species are very heterogeneous, 

 and it may be that several different forms have been classified 

 together. 



What especially characterizes this species is that the rami- 

 fication has more or less a tendency to be verticillate ; this being 

 especially the case in the var. gelatinosa. 



Most of the specimens referred to this species show upon a 

 transverse section of the young thallus a relatively distinct central 

 cyhnder. In older parts of the thallus it is more indistinct or 



