F. Børgesen: Rhodophyceæ of the Danish W. Indies. 



357 



Subfam. 2. Tylocarpeæ. 

 Gymnogongrus Mart. 



1. Gymnogongrus tenuis J. Ag. 



J. Agardh, in Act. Holm., 1849, p. 88; Spec. Alg., vol. II, p. 319; 

 Epicr., p. 211. 



Chondrus tenuis J.Ag. in Kützing, Spec. Alg., p. 7.36; Kltzing, Tab. 

 Phycol., vol. 17, pi. 52. 



The specimens form dense bushes upto 5 — 6 cms height. The 

 thallus is of a firm and cartilaginous consistency; it is flat and repeat- 

 edly forked (Fig. 352). 



From a transverse 

 section of the thallus 

 it appears that it con- 

 sists of a parenchymatic 

 tissue, whose cells are 

 largest in the middle 

 (about 40 — 50 ja lat.) 

 smaller outwards. The 

 cortical layer consists 

 of small cells with 

 thick walls placed in 

 rows forming together 

 a very firm tissue. It 

 is surrounded by a 

 rather thick cuticle. 



In some of the specimens, collected in March, cystocarps were 

 found forming proportionately large, flat, roundish-oval projecting 

 discs on the one side of the thallus. 



The plant is a littoral alga. It was growing on stone-quays etc. 

 together with Grateloupia, Ulva etc. near the surface of the sea in 

 places where the waves constantly dash the stones and where the 

 water was much polluted. 



St. Thomas: The harbour of Charlotte Amalia. 

 Geogr. Distrib.: West Indies, Mexico, La Guayra. 



Fig. 352. Gymnogongrus tenuis J. Ag. 



Part of the thallus. 



(About -li). 



