CYCLIC ACTIVITIES OF LIFE 251 



watches in the dark room, as twilight is 

 falling outside, although the organisms have 

 not been exposed to light all day, one observes 

 the little lamps light up and flash out one 

 by one like coruscating diamonds in the 

 darkness, till the whole dish is studded with 

 flashing and disappearing light, a glorious 

 sight in the darkness and stillness. 



At the daybreak, the series of changes 

 are the reverse of those witnessed at dusk ; 

 if the dish containing the organisms be 

 observed in the dark room about an hour 

 before sunrise, it will be seen that at first 

 the organisms are still flashing out brilliantly, 

 but about half an hour before sunrise, the 

 number of flashes begins to diminish rapidly ; 

 at sunrise there are hardly any showing, and 

 half an hour later even violent stirring will 

 not produce a single sparkle. The most 

 remarkable thing of all is that this regular 

 daily phasic action is kept up for as long as 

 fourteen days, by which time the organisms 

 have perished in captivity. Regularly every 

 evening the lights come out, and as regularly 

 every morning they are extinguished, although 

 all the intervening time the tiny living 

 creatures have been kept in darkness. 



A similar diurnal rhythm has been observed 

 for shorter periods in plant leaves which alter 



