SOIL ALGAE 



303 



(8) During a very long drought the resting cells of algae below 

 the surface will still survive. 



Apart from the moisture relations there are also other factors 

 that may be involved. Diatoms can survive very low temperatures, 



100 



80 

 60 

 40 

 20 



c. ...Unaffected A_ ^b^^^S 



blcohtlu bLi.sm.oly6<sd. 



StTSrvgl-y pU-amolUied 



4-1 

 o 



o 



t-t-. 



o 



d 



c 



5 days 



lOOr 



2c/a 



lys 



3 days 



Length of exposure to drought 



Fig. 192. Effect of exposure to drought on A, Hormidium\ B, "Hormidium" stage 

 of Prasiola; C, Zygogoniuyn ericetorum. (After Fritsch and Haines.) 



— 80° C. for 8 days or — 192° C. for 13 hours, whilst dry spores of 

 Nostoc sp. and Oscillatoria brevis can survive —80^ C, though if 

 they are moist a temperature lower than — 16° C. will kill them. As 

 the vegetative filaments of Xostoc die after four days at —2 to 



— 8° C. this genus must survive severe winters in the form of 



