OF THE FILAMENTOUS ALG^E. 75 



exhibit a peculiarity in the contraction of their cell walls 

 when they are drying ; that is to say, the latter do not 

 return to their former state when soaked in pure water ; 

 but if a little muriatic acid or caustic potash be added to it, 

 the cells immediately swell out to their original form. 

 Should the filaments be encrusted with crystals of lime, 

 they may generally be got rid of by means of dilute 

 muriatic acid. 



There is one genus, Psichochorium, which has the 

 remarkable property of depositing lime in the joints of its 

 filaments. Special care must be taken to get rid of this 

 when the specimens are beiDg prepared, as, in case of their 

 being left behind, the very parts become obscured and 

 useless on which the generic characters depend. 



