Parthenocarpy 217 



dence (Miiir, 1951) has indicated that the enzymatic production of 

 auxin is activated by pollination, possibly by increasing the avail- 

 ability of some precursor of auxin. 



Thus it can be seen that, when fruit-set occurs by pollination, a 

 source of auxin is made available to the ovary and stimulates the 

 commencement of growth into a fruit. In parthenocarpic frtiit-set, a 

 sufHcient source of auxin is supplied either by natural production in 

 the ovary or by the apj^lication of auxin. 



The Role of Nutrients 



Fruit-set in general, either parthenocarpic or by pollination, re- 

 quires something more than auxin alone. Leopold and Scott (1952) 

 demonstrated that there is a requirement for organic nutrients or 

 substrates for growth. They have shown that in the tomato there is 

 a requirement for mature leaves, lor with all the mature leaves removed 

 from the plant there is no fruit-set. The presence of increasing niniibers 



NUMBER OF MATURE LEAVES 



Fig. 92. The effect of leaves on tomato plants in permitting fruit-set as a 

 result either of pollination or of treatment with auxin, 20 mg./I. p-chlorophenox- 

 yacetic acid (Leopold and Scott, 1952). 



