FELIX G. GUSTAFSON 355 



necessary for the enlargement of the ovary into the ripe fruit. When he 

 removed the ovules little growth took place; but if lanolin containing 

 indoleacetic acid was placed in the locular cavity in place of the ovules 

 nearly normal growth occurred. Gustafson (6) corroborated this finding 

 with the crook-neck summer squash. He cut the ovary from unopened 

 flower buds at different distances from the base. By this procedure the 

 base was left without any ovules or with smaller or larger numbers 

 depending upon the position of the cut. When no ovules were included 

 in the ovary the growth was slight, and the amount of growth increased 

 with the number of ovules left. Indolebutyric acid in lanoUn smeared 

 on the cut surface caused the portion of the ovary without any ovules 

 to grow as much as it would have grown in a normally fertilized ovary 

 (Fig, 6). Both of these investigators emphasized the importance of 

 ovules and seeds in the development of fruits. Meyer (i6) and also the 

 writer (8) have shown that ovules, placentae, and seeds are much richer 

 in growth hormones than other parts of the ovary or fruit. 



As a result of these investigations the theory was developed (7) that 

 fruit growth is initiated by the growth hormone brought into the ovary 

 by the pollen tubes carrying the sperm nuclei into the embryo sacs. In 

 plants like the navel orange, lemon, and grape where seedless fruits 

 are normally produced, the growth-hormone concentration in the ovary 

 was found to be greater than in similar varieties, which required poHina- 

 tion or fertilization for fruit production. Van Overbeek (24) has ques- 

 tioned the suggestion that growth hormones are supplied to the ovary 

 by the pollen tubes, and he suggested the alternative that pollen tubes 

 might carry into the ovary enzymes, or more specifically, prosthetic 

 groups which would form enzymes, that acted on bound growth hor- 

 mones to release the active form. 



REFERENCES 



1. Blondeau, R. and Crane, J. C, Science, 108:719 (1948). 



2. DoLLFUS, H., Planta, 25:1 (1936). 



3. Gardner, F. E. and Marth, P. C, Botan. Gaz., 99:184 (1937). 



4. Gardner, F. E. and Kraus, E. J., ibid., 99:355 (i937)- 



5. Gustafson, F, G., Proc. Nat. Acad. Sci. U. S., 22:628 (1936). 



6. , Am. J. Botany, 25:237 (1938). 



7. , ibid., 26:135 (1939). 



8. , ibid., 26:189 (1939). 



9. , Proc. Am. Soc. Hort. Sci., 38:479 (1940). 



