522 FUNDAMENTALS OF FRUIT PRODUCTION 



stage for fertilization. In many cases several weeks between the time of 

 pollination and fertilization are required for the ovules to reach maturity. 



Kusano,^^ who studied the influence of pollination in stimulating the develop- 

 ment of the ovary and fruit in Gastrodia, found that many fruits would develop 

 in this genus when no pollination occurred. These parthenocarpic fruits were 

 normal in appearance, .though somewhat below the average in size. Seeds were 

 formed but they were without embryos and the number of these imperfectly 

 formed seeds was usually below that in fruits resulting from ordinary pollination. 

 When Gastrodia flowers are poUinated with pollen of Bletia, another orchid, 

 fruits likewise developed but they were much larger than the parthenocarpic 

 fruits developing without pollination, though they too were without embryo- 

 containing seeds and presumably no fertilization had occurred. Fruits of the 

 first category, that is, those developing without the stimulus of pollination, were 

 classed as instances of vegetative or autonomic parthenocarpy; those of the 

 second class were considered instances of stimulative or aitionomic partheno- 

 carpy. Commenting upon the results of some of his experiments, Kusano*^ 

 remarks: "As regards the parthenocarpic development by the foreign pollen 

 two points may be worthy of consideration. First, the size of the resulting 

 fruit may depend on the intensity of the stimulus. This is evidenced by the 

 experiment with the Bletia-poUinium; pollinated the day of bloom, the poUin- 

 ium sends out massive tubes, leading the fruit to maximal growth, but the 

 delayed pollination brings about a feebler development of the tube, perhaps 

 owing to a certain modified condition of the stigma, and consequently smaller 

 fruits result. Further, the poUinia of other orchids yield smaller fruits than the 

 Bletia-pollinium, in conformity with the feeble development of the pollen-tubes. 

 Secondly, it may be most probable that the size of the fruit correlates with the 

 duration of the stimulus acted upon. The product of the normal-sized fruit by 

 crossing Bletia appears to be due to the longevity of activity of the pollen-tube, 

 remaining alive and vigorous far beyond the period of maturation of the fruit, 

 and thus exerting the stimulus unceasingly upon the ovules and ovary throughout 

 the interval of their complete development. ... As far as observed in 

 Gastrodia, we are led to the view that the ovarial development is correlated 

 with the embryogenic development of the ovules when the tube of its own 

 pollinium is concerned, but when it is induced by the foreign pollen tube, it is 

 likely comparable to the gall formation by the action of fungi or insects. So that, 

 though the kind of the stimulus is unknown, whether chemical or mechanical, 

 we may ascribe the resulting effect to an incessant stimulus of suflScient intensity." 



The Effect of Certain Stimulating Agents on Fruit Setting. — It 

 has long been known that the fruits of certain species which seldom or 

 never develop parthenocarpically can be made to set occasionally by 

 treating the stigmas with certain stimulating agents other than pollen. 

 Indeed the use of Lycopodium spores, mentioned in a preceding paragraph, 

 may be regarded as a stimulating agent of this character. Hartley^^ 

 secured a partial set of fruit in tobacco by treating receptive stigmas with 

 magnesium sulfate and other chemicals. The seeds of these fruits 

 were poorly developed and without embryos. Wellington, ^^'^ working 

 with the same species, obtained some fruits, likewise without good seeds, 



