KENNETH J'. THIMANN AND GEORGE M. CURRY 617 



tiles, it was louiul that about lAvicc as much auxin had come from 

 the shatled side as liom the lighted side. Similar results have been 

 obtained by several workers since. A recent more extensive rejjetition 

 of these experiments (Briggs, Tocher, and Wilson, 1957) is shown 

 in Fig. 1. rhc figure brings out four relevant points: 



(1) illumination of the tip does not influence the total auxin 

 production; 



(2) slitting the basal end of the tip section — necessary to separate 

 lighted and shaded halves — does not of itself affect the total 

 auxin production; 



(3) the yield of auxin from the lighted side decreases and that 

 from the shaded side increases (confirming the older observa- 

 tion) ; but 



(4) this difference does not occur when the coleoptile section 

 is slit all the way to the top. 



The first and last points show that simple destruction of the auxin 

 by light is not the explanation of the uneven distribution, but that 

 it depends on lateral movement of the auxin from the lighted 

 towards the shaded side, which is demonstrated in e and /. This con- 

 clusion had in fact been reached much earlier as a result of com- 



0) 



r\ 



255' 



DARK 



b) 



/T\ 



24 







d) 



/T\ 



: I 1 



26 2" 23.4' 



LIGHT 



e) ^ f) 



31 0' 



12 5' 



g) A h) 



^\ 



C 



23.0' 24.7' 



Fig. 1. Difliision of auxin into agar in 3 hours from corn coleoptile tips. Each 

 figure, the curvature produced on standard decapitated ATcna bv 3 corn tips. 

 a. intact, dark; b, totally slit, dark; c, intact, light; d, totally slit, light; lower left: 

 slit only at base; e, dark side; /, light side; lower right, totally slit; g, dark side; 

 h, light side. (From Briggs, Tocher, and Wilson, 19.57). 



