190 JACQUES LOEB AND HARDOLPH WASTENEYS 



33 Hefner candle lamp. 50 cm. distance. July 15, 1916 

 20 minutes exposure. 



Number of total hydranths = 58 

 At start bent backwards = 8 ( _ -,(• 

 At start bent forwards = 8/ 



Hence 42 were apj^arently available for the experiment. At the end (after 

 20 minutes exposure and 2 hours in dark) bent forwards 13, i.e. 13 — 8 = o actu- 

 ally bent to light; hence -{^ = 11.9 per cent reacted of apparently available num- 

 ber of polyps. 



After long exposiu-e'' to same lights 41 bent forwards, showing that 33 were 

 actually available for experiment. 



Hence in 20 minutes ^\= 15.1 per cent bent to light. 

 40 minutes c.rposure. 



Total number of hydranths = 87 

 At start bent forwards = 15\ _ „ 

 At start bent backwards = 13/ 



Hence 59 were apparently available. At the end of experiment, bent forward 

 38; hence 38 — 15= 23 bent imder influence of light, i.e., fir = 39 per cent of 

 apparentlj' available. 



After long exposure to same light, 64 l)ent forward. G4 — 15 = 49 actually 

 available. 



Hence in 40 minutes f f = 47 per cent bent to light. 



Fifty minutes exposure gave the same result. 



This shows that with the time of exposure the percentage of 

 bending polyps increases until finally all the available polyps 

 bend. The example chosen also shows that it is sometimes 

 impossible to obtain 50 per cent of polyps to bend. The varia- 

 ation in the condition of material makes a large number of 

 experiments necessary'. 



In our experiments we exposed in the majority of cases only 

 28 minutes at a distance of 50 cm., in order to avoid the possi- 

 bility that all the available polyps underwent bending; since in 

 this case the observed ratio of 1 : 1 : 1 for the three distances 

 would have been meaningless. In all the experiments the num- 

 ber of polyps which bent was always smaller, and generally 

 considerably smaller, than the number of available polyps. 



The following table gives a summary of the results. The first 

 three columns give the times of exposure for the three distances 

 of the source of light, selected, as stated, on the assumption that 



* Usually from two to three hours. 



