Parthenocarpy 221 



caprification (a specialized lype oi pollination) by the fig wasp. While 

 auxins in general, such as 2,4-D and other phenoxyacetic acid deriva- 

 tives, are very effective in this regard they have the disadvantage of 

 producing seedless figs. Because consumers are so used to the presence 

 of seeds in figs, it has become necessary to seek other auxins which 

 might induce parthenocarpy and permit the development of at least 

 the endocarp or seed coat. It has been found that benzothiazole-2- 

 oxyacetic acid, a weak auxin, is capable of setting fruit in the fig and 

 causing the development of the seed coat as well (Crane, 1952). This 

 is a rather remarkable instance of different morphological responses 

 to different auxins. 



A good many other species of plants have been successfully 

 forced to set fruit parthenocarpically by auxin application. These in- 

 clude many members of the Cucurbitaceae such as squash, pumpkin, 

 watermelon and cucumber, several members of the Solanaceae such as 

 tomato, tobacco, pepper and eggplant, and the holly, okra and fig. 

 Each of these are fruits with many ovules per ovary. 



Techniques of Application 



Early experiments on fruit-set with auxins were carried out by 

 severing the style and placing lanolin paste of auxin on the stump of 

 the style. This exacting process has been found to be unnecessary, and 

 instead a simple aqueous spray applied to the flower is entirely effec- 

 tive and much more convenient. It is not essential for the auxin spray 

 to reach the stigma, the ovary, or even the face of the tomato flower, 

 for it has been shown that auxins applied to the back of the flower, 

 the pedicel, or even parts of the stem could induce fruit-set (Zalik 

 et al, 1951). Randhawa and Thompson (1948) have succeeded in in- 

 ducing fruit-set by applying growth regulators to the soil below the 

 plant. This soil application is probably effective by translocation of 

 the auxin through the transpiration stream to the floral parts. 



The use of volatile esters of auxins to set tomato fruit in green- 

 houses without individual treatment of flower clusters has been used 

 with moderate success (Zimmerman and Hitchcock, 1939). A quarter 

 of a gram of a volatile ester of PCA per 1000 cubic feet of greenhouse 

 space was found to be effective. Application in aerosol dispensers has 

 been found to be both effective and convenient, using 1000 mg./l. of 

 an ester derivative of BNOA or PCA (Hewlett and Marth, 1946). 

 Another technique which has been used successfully is the incorpora- 

 tion of the auxin into a fungicide dust. This has been found to be 

 especially effective for snap beans using 2 p. p.m. 2,4-D (Wittwer and 

 Murneek, 1949). 



