JOHN W. MITCHELL ^5^ 



this response is similar to that which occurs in stems of plants treated 

 with these substances (21,40,53). 



It was recently found that the accelerating effect of 2,4-D on the 

 ripening of bananas is greatly reduced by the lack of adequate aeration 

 following treatment (29). Although the reason for this is not understood, 

 the results indicate that in the absence or the presence of certain gases, 

 tissues of fruits such as the banana may be relatively insensitive to 2,4-D. 



Recently attention has been directed toward the effect of growth- 

 regulating substances on the vitamin content of plants. In recent experi- 

 ments with beans the initial vitamin C content of the pods was not 

 affected when the plants were sprayed with 4-chlorophenoxyacetic acid. 

 The rate at which the vitamin was broken down during storage of the 

 treated fruits was, however, much slower than for untreated ones. This 

 effect was thought to be indirect since the growth regulator increased 

 the storage hfe of the pods (36). 



According to recent tests with bean plants, application of 2,4-D 

 brought about reduction of thiamin, riboflavin, and nicotinic acid in 

 the leaf tissues (26). Stems of treated plants, on the other hand, con- 

 tained higher concentrations of thiamin, riboflavin, nicotinic acid, and 

 pantothenic acid than did comparable parts of untreated ones. The 

 concentration of carotene in both leaves and stems was depressed by 

 2,4-D, while the concentration of pantothenic acid was increased in 

 stem and leaf tissues by its appHcation. These data indicate clearly that 

 2,4-D brought about definite shifts in the concentrations of certain 

 vitamins between stem and leaf tissues, but information on its effect 

 on total vitamin production per plant is not at present available. 



2,4-D has increased the protein content of wheat seedlings when 

 appHed in amounts ordinarily used for weed control (13). Increases of 

 approximately 5 per cent or less in the protein content of seeds have 

 been reported on the basis of field tests. Smaller increases were readily 

 observed in greenhouse experiments, but in most instances these were 

 accompanied by a depression in the yield of wheat seeds (33). The effect 

 of growth-regulating substances on the chemical composition of fruits 

 and seeds offers a relatively new and fertile field of study, which is just 

 now beginning to receive the attention it deserves. 



