THE BLUE-GEEEN ALGM 



25 



TiOr. 9. — Glcbooapsa Poly- 



DEEMATIOA (StRASS- 



burger). Highly Mag- 

 nified. 



the famous eruption of Krakatoa, whose streaming lavas 

 destroyed all vestiges of life in the area over which they 

 poured, the first plants to colonize 

 the lifeless lava-waste were Blue- 

 Green Algae. They have been 

 recognized as the first plant 

 colonists of fresh lavas in other 

 places. In 1874 a species {Der- 

 mogloea Limi) appeared in the sea 

 off the Adriatic coasts, and multi- 

 plied so extensively that the fishing 

 industry was seriously hampered, 

 but after six weeks the nuisance a. Beginning to divide ; 



suddenly dis- ^' ^^°r*ly ^^^^ division ; 

 - O, a later stage. 



appeared. 



The simplest Blue-Green Algse are 

 included in the family Chroococ- 

 cacese ; they are all one-cell forms 

 which have the habit of cohering 

 in colonies. One genus, Gloeocapsa 

 (Fig. 9), estabhshes itself in small 

 gelatinous colonies on damp walls 

 and rocks, and not infrequently on 

 hot-house window-panes. Stagnant 

 4, Portion of a filament; Water is frequently covered with 

 h, h, hetero-oysts; sp., films of Merismofedia. The method 

 of multiplication is that of simple 

 fission. 



In NostoG (Fig. 10) we have a 

 filamentous form. It occurs com- 

 monly in round, bluish - green, jeUy-like masses on 

 damp soil, in farmyards, on walls and garden walks. 



4 



EiG. 10. — NosTOC 

 LiNOxn. X 470. 



sp., spores; B, germin- 

 ating spore ; 0, young 

 filament from spore ; 

 ruptured cell-wall of 

 spore seen at ends. 



