352 PLANT GROWTH SUBSTANCES 



fruits of the tomato and many other plants by applying synthetic growth 

 hormones to the pistil. The general procedure was to mix the hormone 

 or growth-promoting substance with lanolin, which was applied to the 

 cut surface of the style of unopened flower buds after the anthers had 

 been removed. To insure diffusion of the chemical into the ovary the 

 style was shortened, and when the style was not too long the stigma 

 was cut to allow easy penetration. The growth-promoting chemicals 

 used in this early work were phenylacetic, indoleacetic, indolepropionic, 

 and indolebutyric acids. Concentrations of chemicals were quite high, 

 sometimes as high as 2 per cent in lanolin, but 0.25 per cent concentra- 

 tions were also used. 



In 1934 Yasuda (28) had produced a few near-normal sized cucumbers 

 by injecting into the young ovaries of the cucumber flowers water 

 extracts of cucumber pollen. As far as is known this was the first success 

 in producing full-sized fruits without seeds by chemical treatment. 

 Other investigators (10) had previously attempted to initiate fruit 

 development by treating the pistil with pollen extracts, but the growth 

 produced was limited. 



In 1937 Gardner and Marth (3) produced parthenocarpic fruits in 

 Ilex opaca and the strawberry with hormone treatment. In the same 

 year Hagemann (11) produced seedless fruits in the gladiolus. Since that 

 time numerous investigators have grown parthenocarpic fruits as a 

 result of treating the pistils with growth hormones, but there have been 

 many failures too. No success has been obtained with such plants as 

 apples, pears, cherries, and peaches. 



A practical use of this method, which was not anticipated in 1936, 

 has also been made. Among the investigators most responsible for this 

 may be mentioned Howlett (12), Strong (22), Roberts and Struck- 

 meyer (20) and Murneek and Wittwer (18). During the dark months of 

 December, January, and February, the setting of tomatoes grown in 

 greenhouses in the northern states is very much reduced due to the 

 poor development of pollen. By spraying the blossom buds with any 

 one of a number of growth-promoting substances the setting has been 

 increased as much as one hundred per cent, and the fruits are of normal 

 or even larger size. Some investigators have added a spreader to the 

 solution, which enables the chemical to remain spread over the surface 

 of the blossom buds after the water has evaporated, but others have 

 dissolved the chemical in alcohol and made dilutions of this concentrated 



