170 



CRYPT0GA2IS 



BLUE-GREEN ALG^ 



409. On wet walls of stone and on undisturbed moist 

 earth may (•ften be found small, rounded, jellylike masses 

 of a greenish or hhiish color. .V bit placed uiuler tlie 

 micrdsciipe shdws a i^reat number of chains of rounded 



cells (Fig. 282), embedded in tlie 

 gelatinous matter. Certain cells 

 of each chain are somewhat 

 larger and lighter colored than 

 the rest. When a chain breaks 

 282. A chain of Nostoc cells: in pieces, as occasionall}' happens, 



/i, hetenicyst : tl, vecpiit .. n j 'i i 



divisious. Separation usually takes place 



next to one of these enlarged 

 cells, or Jteteroci/st^. The fragments finall}' develop into 

 chains of tlie migiiial character. The cells increase in 

 number by traiis\'erse di\ision (Fig. 282, cl). Cell divi- 

 sion is, ill fact, the ordinary process by which the jjlants 

 of this group multiply. 



410. If the snlistratum on which the plants are grow- 

 ing dries up, the imesting mass of gelatinous sulistance 

 hardens in propiutidii as it parts witli water, and so lie- 

 comes a pr(itecti\e coating whicii enables tlie plant to 

 withstand extreme drciiight. 



411. The plant hen; described and iigured (Nostoc) is 

 representati\e nf the lUiie-green jVlgae in color, iu the 

 filamentous ari'aiigement of tlie cells, in the method of 

 multiplication by transverse lission, and in tlirowing off 

 macilaginous matter from the walls to form sheaths and 

 embedding masses. In some species, however, the cells 

 are fnund in small groups, not tilamentous ; and in others 

 the gelatinous coating is either very thin or entirely 

 wanting. 



412. Oscillatoria (Fig. 283) i.*, like niaiiy of the group, often 

 aquatic, eitliei- lloaling freely or gatlieved in small tutts. The tllameuts 

 have a cliaracteristic motion of bending slowly from side to side — 

 wlience the name Oscillatoria. They also possess some means of 

 locomotion, hy wliidi tliey slip along over tlie snfjsti-atum, while at llie 

 same time slnwly ^H^-|Jlving upon the louger axes of the filaments. 



