1526 A TEXTBOOK OF THEORETICAL BOTANY 



of the cluster, which alone produce the fruit, are pistillate and are unpollina- 

 ted, whereas the upper flowers, which contain stamens, do not form usable 

 fruit. Other fruits which are naturally parthenocarpic include several seed- 

 less varieties of the Orange {e.g., Navel and Valencia Oranges), seedless 

 varieties of Cucumber, of the Persimmon {Diospynis virginiana) and some 

 seedless Grapes such as Black Corinth and Thompson Seedless. The Apple 

 and the Pear will sometimes form fruits without pollination if the trees are 

 vigorous and pollination is wholly prevented. In the Fig, the variety 

 Kadota and other Californian varieties are completely parthenocarpic, 

 while the Calimyrna, a Smyrna Fig, is non-parthenocarpic. Tomato fruits 

 may sometimes be produced without pollination but they are quite small. 



The second condition is that in which pollination provides the stimulus 

 to fruit formation but without fertilization or the production of seed. The 

 leading case here is the Pineapple, which in cultivation is normally self- 

 pollniated, but is self-incompatible. Seed formation is therefore a rarity 

 but it occurs if plants are artificially cross-pollinated. The wild plant seems 

 to be self-fertile and self-fertile mutants have occurred in cultivation, but 

 offer no commercial advantage. Seedless parthenocarpic fruits are also 

 formed by many self-incompatible Pears after self-pollination. The seedless 

 Pears are smaller than the normal fruits at the carpel end, but they contain 

 more sugar. The Peach also produces parthenocarpic fruits after incom- 

 patible pollination, but the fruits are much smaller than normal and ripen 

 more slowly. 



Lastly there is the condition of induced parthenocarpy which compre- 

 hends all the cases where sterile fruits result from artificial treatment. 

 Various procedures have this effect. Foreign pollen may be used, which 

 stimulates fruit development though it has no power of fertilization. Some 

 examples of success by this method have been recorded among the Solan- 

 aceae and Cucurbitaceae and in the Grape. Aqueous extracts of pollen, 

 even of foreign pollen, injected into the ovary have sometimes resulted in 

 fruit growth in Solanaceae. 



Most of the experiments have been in the use of giowth-promoting 

 substances of the hetero-auxin class. Parthenocarpic fruiting in Tomato 

 can be very successfully induced by spraying the flowers with alpha- 

 naphthaleneacetic acid, and in Calimyrna Figs by para-chlorophenoxyacetic 

 acid or gamma (indole 3) n-butyric acid. Most of the fruits so produced, 

 in Tomato, Strawberry, Lilhim regale and others, do not differ in size or 

 external appearance from the normal fruits, although they are seedless, 

 but in the Calimyrna Figs the fruit is somewhat compressed longitudinally. 

 In the Kadota Figs fruits may be rendered fertile by artificial pollination 

 although they are naturally parthenocarpic, and the fruits difter markedly 

 from each other. The pollinated fruit is greenish, ribbed and has a dull 

 surface but it has a richer or sweeter flavour than the normal parthenocarpic 

 fruits which are yellow, smooth and shiny. 



Although it would seem that naturally parthenocarpic ovaries contain 

 sufficient growth-promoting substance to prevent the formation ot an 



