150 THE FLOWERING PROCESS 



were dependent upon some exogenous factor resulting from the 

 earth's rotation, then this unfortunate creature should be unable 

 to measure time. Hamner obtained a grant from the National 

 Science Foundation and went to Antarctica during the Antarctic 

 summer of 1960-61. He took with him several organisms which 

 measure time, including both plants and animals. He placed them 

 on turntables which held them steady in space, which rotated in 

 the same direction as the earth, or which did not rotate at all. In 

 every case the organism continued to measure time. His experiment 

 was carried out virtually on the south pole itself, so the rotation 

 of the earth could be nulhfied. The magnetic pole, however, does 

 not coincide with the rotational pole of the earth, so it might be 

 objected that Hamner's organisms were still in a fluctuating 

 magnetic field, even though other effects of the earth's rotation had 

 been eliminated. At any rate the results failed to support exogenous 

 timing, and Hamner had some extremely interesting months in 

 carrying out his project. 



Brown's experiments are valid, whether his interpretation is or not. 

 So how are we to understand his data ? Perhaps we can say that the 

 living organism does have an endogenous timing mechanism, but 

 that it is in addition able to respond to changes in very subtle 

 environmental factors. It is possible that we have not yet recognized 

 the factors, and it is highly probable that we have not yet recognized 

 the mechanism of response. Thus is may be possible to superimpose 

 an exogenously controlled periodism upon the normal circadian time 

 measurement of living organisms. 



3. Where is the Biological Clock Located? 



Single-celled organisms are frequently capable of measuring time, 

 as are the cells of plant and animal tissue cultures derived from multi- 

 cellular organisms. We may conclude, then, that there are no special 

 organs set aside within the plant or animal for the measurement of 

 time, but that this phenomenon is a function of cellular activity itself. 



Where is it located within the cell? Might it be in the nucleus 

 itself? Bunning's students report a change in nucleus volume which 

 seems to follow a circadian rhythm. The period of leaf movement 

 can be changed by treating the plant with chemicals which are known 

 to have an effect upon the nucleus. These include colchicine and 

 urethane (ethyl carbamate). Among many other compounds which 



