ROBERT M. MUIR 359 



These results indicate that following pollination and fertilization an 

 auxin production mechanism is established in the ovary which brings 

 about the enlargement into the fruit. 



A similar sequence of changes in hormone content of the ovary occurs 

 in Heliopsis laevis according to Soding (17). The amount of diffusible 

 auxin in the flower head increases from the bud stage until the flowers 

 begin to turn yellow then decreases until no detectable auxin is present 

 when the flowers are fiilly open. After fertilization diffusible auxin 

 again is present in the flower head but the amount decreases as the 

 fruits mature. Soding inferred that the free, diffusible auxin of the young 

 fruit is transformed into the immobile reserve auxin of the seed. 



According to Hatcher (7) no diffusible auxin is found in the rye grain 

 until three weeks after pollination whereupon a marked increase occurs 

 with a maximum at five weeks, and then a steady decline follows to 

 maturity. He concludes that the growth rate of the rye grain is not 

 related to the amount of auxin present in the grain since very little 

 auxin is present during the first three weeks of its development and 

 maximum amounts are present when its growth has ceased. However, the 

 most important auxin-growth relationship in the development of the 

 fruitof A7ro//a«j appears to be the initiation of the enlargement associated 

 with the presence of relatively large amounts of diffusible, fi-ee auxin as 

 shown in Table i . Enlargement of the pollinated pistil begins promptly 

 when the pollen tubes reach the ovules (approximately 45 hours after 

 pollination) at which time there is a large increase in diffusible auxin, and 

 during the following 40 hours the ovary nearly doubles in size whereas 

 the ovarv of the unpoUinated pistil enlarges very little. It should be 

 realized that changes in the auxin content of a head of flowers or a 

 capsule containing hundreds of ovules represent composite effects of 



TABLE 1 



Average length of ovaries of Nicotiana tabacum 



Hours after anthesis Pollinated L'npolxjnated 



15 

 36 

 46 

 ^ 



85 



