ENDOGENOUS DIURNAL PERIODICITY 



519 



length of period. It seems that most of the metaboHc poisons inhibit 

 only the special process which depends on the clock, but do not 

 inhibit the clock itself. This becomes especially clear from experiments 

 of BUhenemann (1955) with Oedogonium. He applied poisons like 

 NaCN, arsenate, 2,4-dinitrophenol, and NaF. Spore discharge in all 

 these cases remains a cyclic process as long as it continues. Moreover, 

 there is no shifting of the phases and no increase in the length of the 

 periods. Our results with Phaseolus are similar (Fig. 13A,B). 



If these poisons have been active for several days and are then 

 removed, the rhythmical process starts once again. And, most interest- 

 ing, there is no shifting of the phases. Maxima and minima occur at 

 the same time that the controls occur (Fig. 13C). That means the 

 clock system is still functioning while the physiological process, 

 normally governed by it, is fully inhibited by poisons. 



I may just mention that we tried in vain to find specific influences 

 of varying ratios of Ca and K or of different pH values. Influences of 

 these factors are always combined with visible injury to the plant 

 (Biinning, 1956a). 



There are, as we found in Phaseolus, distinct influences of colchicine 

 and urethane. Alcohol, ether, and especially digitonine can also cause 

 irregularities of the internal clock (Fig. 14). Many other substances, 



Phaseolus. Digitonine 0,02% 



Fig. 14. Phaseolus multifioriis, leaf movements in continuous light. 

 Effect of 0.02% digitonine, offered via the transpiration stream. 



such as all the different plant hormones (Ball and Dyke, 1956) 



and alkaloids, have no specific influence (Bunning, unpublished data). 



By applying a poison like urethane it is possible to observe a 



phenomenon which reminds us of what happens after a period of 



