SECT. II. 



OSCILLATOR!^ 



215 



liar mode 

 alternate 

 species of 



In the compound gelatinous Oscillatorise, the jelly is 

 of ver^ different degrees of tenacity. The mass of the 

 Dasygloea is so slippery that it can scarcely be taken 

 hold of; Rivularia nitida (fig. 19) is equally so, its tubes 

 being so thick and tender. Many species of the genus 

 Bivularia have a pecu- 

 of oblique 

 branching ; 

 that genus 

 crrow on the stems of 



o 



aquatic plants, on rocks 



in rapid streams, on 



cliffs when washed by 



cataracts, or sometimes 



in calcareous water, in 



consequence of which 



crystals of carbonate of 



lime are deposited on 



their substance. The 



Rivularia nitida occurs 



among Algse exposed at 



low tides, and a species 



of another genus floats 



on fresh-water lakes like F . g 19 Thieads ot ElviUaria niuda _ 



green stars. 



The Oscillatorige are found in every part of the world, 

 most abundantly in the temperate zones. They chiefly 

 inhabit fresh water, but these minute plants attain their 

 greatest size in the sea. . Numerous species grow in 

 warm springs, and one species, Trichodesmium ery- 

 thrseum (fig. 20), spreads for many square miles over 

 the surface of the Indian seas in faggots of red-brown 

 threads, like fragments of chopped hay ; the same species 

 is said to abound in the Red Sea also. 8 



f Cryptogamic Botany.' By the Key. M. J. Berkeley. 



