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



29 



in the middle. The union of the filaments is due to a tough 

 mucilage which holds them together. But after boiling the plant 

 for a short time in water the filaments easily separate in such 

 a way that their mode of growth was observable. 



As the figures (Fig. 18 a, b, c) show the central filaments 

 increase by means of intercalary growth. Each filament termi- 



Fig. 18. Castagnea Zosleræ (Mohr) Thur. 



Summits of filaments showing way of growing. 



(a, c, about 150 : 1 ; b, about 200: 1). 



nates with a long hair, the cells of which are long and colourless, 

 at the upper end being shorter and shorter towards its base. 

 Here we have the growing point from below which the cells of 

 the main filaments are formed, and above those of the hairs. At 

 their base the hairs have a thin sheath. 



When this method of growth has continued for a time the 

 end of the filament is bent out laterally and a side branch similar 



