EXPERIMENTAL EMBRYOLOGY 399 



proved conclusively that pollen has a definite influence on the 

 growth of the ovary which is independent of fertilization or matu- 

 ration of seeds. 



More extensive studies on the role of pollination in fruit growth 

 — without the accompanying fertilization — were made by Yasuda 

 (1930, 1933, 1934, 1939). Although all plants did not react favor- 

 ably, he achieved an appreciable measure of success with certain 

 members of the Solanaceae and Cucurbitaceae. His experiments 

 and observations may be summarized as follows : 



1. Castrated flowers were treated with pollen of the same species 

 in different stages of maturity. As was to be expected, ovaries 

 treated with mature and viable pollen developed into normal fruits; 

 but immature or overmature pollen also, although incapable of 

 causing fertilization, frequently stimulated fruit formation, with 

 the difference that in this case the fruits were devoid of seeds. 



2. In a second lot the same procedure was followed using foreign 

 pollen, i.e., pollen from another plant belonging to the same or a 

 different family. When fruits were produced, these were either 

 devoid of seeds or showed only abortive ones. 



3. The styles of a number of flowers of Solanum melongena were 

 cut off at their junction with the ovary at different intervals after 

 pollination. When the operation was sufficiently delayed, the pol- 

 len tubes were able to reach the ovules, resulting in fruits with 

 viable seeds. But if it was performed at a time when the pollen 

 tubes were close to the base of the style but had not entered the 

 ovary, the fruits were seedless. In control experiments, in which 

 the styles were removed as before but the stigmas were left unpol- 

 linated, no fruits of any kind were produced. 



4. In a fourth set of experiments, the styles were cut off as before 

 but regrafted on the ovaries with an intervening layer of gelatin. 

 The plants were then divided into two lots, one lot being self -pol- 

 linated and the other left unpollinated. The ovaries of the former 

 occasionally developed into seedless fruits, but the unpollinated 

 ovaries usually failed to grow further. When they did produce 

 fruits on some very rare occasions, these were much smaller than 

 those of the first lot. 



5. Finally, pollination was entirely omitted and in its place aque- 

 ous extracts of pollen were injected into the ovary. Solanum me- 

 longena ovaries, injected with an extract of Petunia pollen, grew to 



