Mast, Orientation in Euglena with some Remarks on Tropisms. (355 



the reaction is approximately proportional to the product of the 

 time and the intensity no matter how either of these factors may 

 vary. In other words, the reaction bears a specific relation to the 

 amount of energy received. This means that a given amount of 

 energy, other things being equal, produces the same reaction no 

 matter whether this energy is applied intermittently or continuously, 

 whether it is received during the period of a second or a day. 

 Since these plant structures can orient in the dark after exposure 

 in intense light for a very short time, and the reactions are 

 apparently in accord with the Bunsen-Roscoe law, Bancroft 

 sees no reason why this law may not hold for fire-flies which also 

 orient in the dark. 



He fails entirely to grasp the fact that the very essence of 

 the law is violated in that the period of illumination necessary 

 for stimulation in the fire-fly cannot be altered. According to this 

 law we should get the reaction if this period is increased provided 

 the intensity is proportionally diminished, as seems to be true 

 within certain limits for plants, but this is not true. 



There is however even a more striking contradiction between 

 the law in question and the orienting reactions of these insects. 

 If the male is one centimeter from the female it requires, for 

 stimulation, the same length of illumination of the same intensity 

 as it does when he is 60U centimeters distant. Thus under the 

 former conditions it requires to produce a given reaction 360,000 

 times as much energy as it does under the latter. How can this 

 be squared with the continuous-action theory if the Bunsen- 

 Roscoe law is to be accepted as a criterion? Moreover the male 

 fire-fly, as stated above, not only orients after the flash of light 

 from the female disappears, but he also remains oriented. How 

 can it be maintained that this animal in the total absence of light 

 is held on his course by the "continuous-action of light" as 

 Loeb's theory demands? On the basis of the continuous-action 

 theory, then, no matter how it be interpreted, I can account 

 neither for the process of orientation in fire-flies nor for the direct 

 course after orientation. 



Bancroft admits that he has been unable to demonstrate 

 that orientation in Euglena is in accord with the continuous-action 

 theory. He was not able to show that the Bunsen-Roscoe law 

 holds for this response. But this theory has failed not only to 

 receive direct support; it does not account for what actually occurs 

 in the process of orientation. As previously stated, if the dorsal 

 surface of a positive Euglena does not face the light after the 

 direction of the rays is changed, there is no response until in the 

 process of rotation this surface comes to be fully illuminated. 

 According to the continuous-action theory the greater the amount 



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