354 PLANT GROWTH SUBSTANCES 



enlarged only slightly. In the crook-neck summer squash (Fig. 3) the 

 ovary developed into a fruit of normal length without fertilization, but 

 when no seeds were pioduced the locular region did not grow as ex- 

 tensively as when seeds were produced. The result was that the partheno- 

 carpic fruits were quite long and thin and showed none of the bulging 

 of the seeded fruit. Figure 4, of buttercup squash, brings out the fact 

 that sometimes the resulting fruit may lack entirely the locules and be 

 composed only of solid flesh. This has also been found in the tomato. 

 The tomatoes lacking locules are, as a rule, considerably smaller than 

 the normal seeded fruits. The writer has also observed this in naturally 

 occurring parthenocarpic avocados, where the stone is lacking. 



Parthenocarpy in nonfleshy fruits is illustrated by the Maryland 

 Mammoth tobacco shown in Figure 5. In this plant the pedicel of the 

 flower is quite stout, and it was possible to inject a solution into the 

 ovary through the thickened pedicel. Ovaries injected with a solution 

 of 0.2 per cent potassium indoleacetate grew more during the first five 

 days after injection than the ovaries from pollinated flowers, and reached 

 nearly the same final size as the seeded fruits. 



Janes (13,14) made a comparative chemical study of parthenocarpic 

 and seeded fruits of the tomato and pepper. He found that in the tomato 

 total sugar and starch was greater in the parthenocarpic fruits. During 

 early stages of development the titratable acidity was the same in both 

 types of fruits, but during the ripening period the seeded fruits had a 

 higher concentration and this was especially noticeable in the locular 

 region. In the ripe fruits the percentage of dry weight was a little greater 

 than in the seeded fruits. The mature parthenocarpic peppers had a 

 slightly higher per cent of dry weight, soluble soUds, sugars, and total 

 nitrogen than the seeded fruits, but the difference was not great. 



Gardner and Kraus (4) found in their extensive anatomical study 

 of the development of the parthenocarpic fruits of Ilex opaca that with 

 the exception of the lack of the seed there was no difference between the 

 seeded and seedless fruits. In tobacco ovaries injected with 0.2 per cent 

 potassium indoleacetate the ovules grew to nearly one fourth the size 

 of ripe seeds and there was some growth in the embryo sac, but no 

 seeds with an embryo ever formed (6). Several investigators have re- 

 ported that the ovules may grow into empty seeds of considerable size 



(27.9)- 

 Dollfus (2) found that ovules supply all or most of the hormone 



