Table 5 . Woloszynskia limnetica 



NB . The pH 8 medium was buffered with TRIS and the pH 6 medium with succinic acid , 

 * hydroxyethyl ethylenediamine triacetic acid 



t a mixture ofOt'- andy^ - glycerophosphates . 



to penetrate the cell . 



In our case we have kept constant the trace 

 metal/chelator mixture and added pH buffers, some 

 of which are metal chelators . Therefore according 

 to b) when one decreases the pH (e.g . when the 

 pH 8 .0 medium is lowered to pH 6 .0 and 5.0), one 

 should add more chelator and when one brings the 

 acid medium to alkaline pH, one should decrease 

 the amount of Chelator. TRIS does not control the 

 availability of trace metals at pH 7 to 8 (Cheno- 

 weth, 1956) nor probably does , TEA. Therefore 

 when TEA is substituted and the alkaline media of 

 Volvox and Phacus are brought to pH 6 .0-6 .5 , 



more chelator should be introduced. This is what 

 we did with the addition of histidine as the buffer 

 for the pH 6 .0-6 .5 zone . However we obtain good 

 growth of Phacus at pH 5 .8 with addition of suc- 

 cinic or malic acids which are poor chelators . The 

 pH 6.0 base of Woloszynskia gives better growth 

 when the pH is raised and succinic acid is re- 

 placed by histidine, TRIS, or glycylglycine. Since 

 the succinic medium is under-chelated, it may give 

 poor growth at pH 5 .6 because it has too much 

 metals; addition of a chelator like histidine could 

 have adjusted the balance, but more growth is also 

 obtained with TRIS, a non-chelator and by glycy- 



92 



