680 



LIGHT AND LIFE 



out sucrose as the basic medium. All cultures were grown in 125- 

 ml erlenmeyer flasks with 50 ml of medium. 



2. pH interaction with EDTA. To see whether the relation be- 

 tween EDTA activity and pH was the same as that observed for 

 L. perpusilla, an experiment analogous to that shown in Fig. 1 Avas 

 performed, using the standard conditions described above. Initial 

 pH values in the two series were 4.1 and 5.0, respectively, since levels 

 below 4.0 proved toxic. Transfers of each entire culture to fresh 

 medium were made on day 4, and dissections on day 1 1 of the experi- 

 ment. The results are shown in Fig. 2, and indicate that the action 

 of EDTA on L. gibba flowering depends upon pW in the same way 

 as that on L. perpusilla flowering, although here the effect is to pro- 

 mote rather than to inhibit. In each case, EDTA is more effective 

 at the higher pH. Since even by the transfer on day 4 the pH in the 

 initially 4.1 medium had risen to about 4.6, while that in the 5.0 

 medium had risen far less, it is clear that the data presented under- 

 estimate the true effect. 



3. Relationship of the EDTA and "old" medium effects. Since the 

 exploratory experiments indicated that the "old" medium effect was 

 manifest in cultures left to grow sufficiently long, it was necessary to 

 determine whether EDTA simply speeds the attainment of the "old" 

 condition or whether it substitutes for it. For this purpose, cultures 



>- 

 < 

 o 



EDTA, M 



Fig. 2. EfTects of two pH levels on EDTA piomotion of flowering of Lemnn 

 gibba G3 in continuous light. Each point represents a value derived from one 

 culture. See Experimental, B3. Exp. 1-22-60. 



