408 Morphogenetic Factors 



variety of plants without causing obvious morphological abnormalities. 

 Plants treated with it tend to lose dominance in their apical buds and 

 show certain other effects (Naylor and Davis, 1950). It seems to inhibit 



Fig. 18-24. Median longitudinal section of young adventitious root apices in rice. Left, 

 of untreated plant. Right, of plant treated with 2,4-D. There is a great increase of 

 periclinal divisions in the latter, which produces massive, abnormal roots. (From 

 Kaufman. ) 



mitosis (Greulach and Atchison, 1953) and also checks the formation of 

 flower primordia in both long-day and short-day plants (Klein and 

 Leopold, 1953; Fig. 18-25). 



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CONC. OF MALEIC HYDRAZIDE 



Fig. 18-25. The effect of maleic hydrazide on the total number of flower primordia at 

 the first five nodes of soybeans. ( From Klein and Leopold. ) 



Substances such as triiodobenzoic acid and coumarin under some 

 conditions increase the effect of auxin and under others markedly inhibit 

 growth. A number of substances occur that inhibit or antagonize auxin 

 action (J. Bonner, 1949) and have been termed antiauxins (Fig. 18-26). 



