378 Morpho genetic Factors 



amount of auxin in developing short shoots and long shoots of Ginkgo and 

 found that elongation of the latter was associated with a sharp rise in 

 auxin content (Fig. 18-1). 



Auxin is also involved in the growth of fruits (Fig. 18-2), though not 

 all the steps in the process are yet well understood (Murneek, 1954; 

 Lund, 1956). There are reviews by Nitsch (1952) and Luckwill (1957). 

 An increase in auxin content often occurs at pollination, again at fertiliza- 



Fig. 18-2. Centers of origin of auxin in the development of a fruit. 1, from mother 

 plant; 2, from pollen; 3, from developing ovules. (From Nitsch.) 



tion, and usually during endosperm growth and the development of the 

 seeds. This increase of auxin in the ovary is often followed by its increase 

 in the pedicel and adjacent regions. 



That fruit development is stimulated by growth substances is made 

 clear by the occurrence of parthenocarpy, or growth of fruits without 

 fertilization and seed development (Fig. 18-3). Gustafson (1936) in- 

 duced parthenocarpy in cucurbits by applying synthetic growth sub- 

 stances to the pistil, and this has now been done frequently with other 



