PERIODICITY IN Hydrodiclijon 



497 



to deduce definite biochemical relations from this coincidence of 

 metabolic and phosphatase activity. We do not know yet whether 

 the periodical behavior of phosphatase can be regarded as specific, or 

 whether more or less the whole enzymic system of the cell is com- 

 pulsorily submitted to such fluctuations of activity. This question is 

 being examined at present in our laboratory (cf. 7). 



80 



70- 



60 



50- 



-r- 



e 



-I— 



lO 



Fig. 3. Periodicity of acid phosphatase (substrate: phenylphosphate) related to 

 protein content in crude extracts of Hijdrodidyon prepared at different times of 

 light and dark periods. Ordinate : y phenol/ 1 00 y prot. ; abscissa : time. 



Periodicity in Hydrodiclijon is not confined to simple metabolic 

 processes. As a result of metabolic periodicity more complex ac- 

 tivities of the cell also exhibit rhythmic variations. Among these, 

 periodic growth rates are most conspicuous. In the light periods, 

 periodicity of growth parallels photosynthetic periodicity almost 

 completely. Accelerations of photosynthesis in continuous light 

 (after-oscillations) correspond exactly to accelerations of growth 

 rates. In darkness the growth rate gradually approaches zero; 

 in continuous darkness immediately following a period of light- 

 dark change we observed two or three small gushes of growth at a 

 time when the light periods had occurred earlier. These growth in- 

 creases, therefore, seem to be induced by the periodic activity of 



