INFLUENCE OF GIBBERELLIN AND AUXIN 331 



tion. However, this early work failed to attract much notice, and 

 further studies along these lines did not start until about 10 years 

 later. In 1949, Bonner and Thurlow, and Harder and van Senden 

 published extensive data on Xanthiiim and on Kalancho'e blossjeldi- 

 ana, which confirmed and extended the earlier observations. Today, 

 the inhibitory effect of applied auxin on photoinduction in short-day 

 plants is well established for several species; some typical data are 

 shown in Table I. 



Table I. Inhibition of Photoinduction in Kalancho'e blossfeldiana by Applied Auxin 



(Harder and van Senden, 1949) 



Once the inhibitory effect of auxin on photoinduction in short-day 

 plants can be accepted as a fact, a number of questions immediately 

 arise: ( 1 ) Is this auxin effect a physiological one? (2) Is it a genuine 

 auxin action? (3) Where, precisely, in the complex process of photo- 

 induction is the point of auxin attack? (4) Does the native auxin of a 

 short-day plant play a part in its photoinduction? And if this is so, the 

 most important of all: (5) what is the role of the native auxin of the 

 short-day plant in photoinduction? 



Question 1 may be answered with "Yes." A significant decrease in 

 photoinduction may be caused by auxin concentrations which have 

 only a slight and passing effect on the growth of the treated plants. 



The answer to question 2 seems also to be in the affirmative. All 

 typical auxins that have been tried (indoleacetic acid, naphthaleneace- 

 tic acid, 2,4-dichlorophenoxyacetic acid, and perhaps one or two 

 more) exhibited an inhibitory effect on photoinduction in short-day 

 plants. Moreover, Bonner and Thurlow (1949) have reported that 

 this effect of auxin can be offset by simultaneous application of an 

 antiauxin. The experimental evidence on this latter point is very 

 limited (see Table II) and ought to be expanded. However, the evi- 

 dence that is available, taken in its entirety, supports the conclusion 



