BLUE-GREEN ALGAE 377 



Anabaena, lead an endophytic life, contributing probably to an 

 irregular nutrition, as in the roots of Cycads. In the establishment 

 of the new Flora of the volcanic Island of Krakatoa (p. 331), Blue- 

 green Algae were among the first colonists, taking their part in the 

 preparation of an organic soil for larger developments to follow. 

 Certain of these Algae allied to Anabaena often appear suddenly in 

 large quantities on the surface of fresh water, causing the pheno- 

 menon known as 4< water bloom," or the ' breaking of the meres." 

 One of these, with a deep red colour {Trichodesmium erythraeum), 

 floats in ocean-waters, and becomes prominent when massed together 

 by wind and tidal streams. It has thus attracted attention in various 

 oceans, and has given its name to the " Red Sea." 



