THE BLUE-GREEN ALG^ 



25 



Fig. 9. — Glceocapsa Poly- 



DERMATICA (StRASS- 



burger). Highly Mag- 

 nified. 

 A, Beginning to divide ; 



B, shortly after division ; 



C, a later stage. 



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- 

 moglcea 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 

 suddenly dis- 

 appeared. 



The simplest Blue-Green Algae are 

 included in the family Chroococ- 

 caceae ; they are all one-cell forms 

 which have the habit of cohering 

 in colonies. One genus, Gloeocafsa 

 (Fig. 9), establishes itself in small 

 gelatinous colonies on damp walls 

 and rocks, and not infrequently on 

 hot-house window-panes. Stagnant 

 water is frequently covered with 

 films of Merismopedia. The method 

 of multiplication is that of simple 

 fission. 



In Nostoc (Fig. 10) we have a 

 filamentous form. It occurs com- 

 bluish - green, jelly-like masses on 

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



Fig. 10. — Nostoc 

 Linceh. x 470. 



A, Portion of a filament ; 

 h, h, hetero -cysts; sp., 

 sp., spores; B, germin- 

 ating spore ; C, young 

 filament from spore ; 

 ruptured cell-wall of 

 spore seen at ends. 



monly in round, 



