F. Borgesen: Phæophyceæ of the Danish W. Indies. 7 



or larger algae, e. g. Codiam. The rhizoids are about 11/^ thick 

 and consist of proportionately long cells. 



In the basal part the main filaments are thinner, reaching 

 only a thickness of about 22 y. ; higher up they grow thicker, the 

 diameter of the cells here being from 35 

 — 45, seldom 50 j«, while their length is 

 about 2 — 3 times as long. In the upper 

 part of the thallus the filaments become 

 thinner again, the cells at the same time 

 becoming proportionately longer. 



The cells are cylindrical or sometimes 

 very slightly barrelshaped ; in the lower 

 part of the thallus their walls are often 

 brownish coloured. 



The lowermost parts of the main fila- 

 ments are not ramified; higher up branches 

 grow out from almost every cell, most often 

 in a secund manner (Fig. 3 a), sometimes 

 alternating. The young branches are some- 

 what attenuated towards their apex (Fig. 

 3 b) and composed of cells which are some- 

 what longer upwards and have fewer chro- 

 matophores. Later on the branches show 

 a marked growing point near their base 

 and terminate with long nearly colourless 

 hairs (Fig. 3 a). The branches are about 

 15— 20 /a thick, the hairs 10— lb /a. 



The chromatophores (Fig. 3 c, d) have 

 the shape of short ribbons in the young 

 cells, in the older they are small roundish 

 discs 1 ). 



Upon their upper side the branches 



again bear smaller ones also terminating 



with hairs and further plurilocular spor- Fig. 4. Ectocarpus Mit- 

 /r ,. o \ rr-,1 i i i chellæ Harv. 



angia (Fig. 3 a). These are developed Base of a plant 



successively upwards from the growing (About 100 : 1). 



point in perfect accordance with those in 



Ectocarpus virescens as pointed out by Sauvageau 3 ). The pluri- 

 locular sporangia are sessile, lanceolate cylindrical, with obtuse 



') Comp. Sauvageau, C, Sur l'Ectocarpus virescens Thuret, (Journal de 



Bot., T. X, 1896, p. 101, fig. 2 B, C). 

 -) Sauvageau, 1. c, p. 101, fig. 2 A. 



