574 



R. M. Sachs and A. Lang 



[li/i^yi ^!:°' \\l^\l 



-- 1 



--2 



-•-3 



Fig. 6. EfFect of 0.1 mg. maleic hydrazide on the number and position of mitotic 

 figures in the pith tissue of Xantluiiiii per 60 n thick median longitudinal section. 

 Each group contained four plants and the diagrams are composites of six median 

 longitudinal sections, each 10 fi thick. Each dot represents a transverse mitotic 

 figure. The boundaries of the vascular tissue and the lower limit of the apical nieri- 

 stem are indicated l)y solid lines. The MH was applied in aqueous solution to the 

 shoot apex (three equal applications on consecutive days). 



whether applied together with or after MH, does not prevent or re- 

 verse the inhibitory effect on cell division. There is some controversy 

 in the literature on the interaction of MH and GA. Bukovac and 

 Wittwer (4) reported that GA overcame the inhibitory effects of MH 

 on the epicotyl growth of beans, and Kato (10) showed with cuctmi- 

 ber seedlings that CiA partially prevented the inhibition of shoot 

 growth by MH. Brian and Hemming (2), working \\ith a variety of 

 peas not responding to GA, concluded that GA ditl not reverse MH- 

 induced inhibition of stem growth and that MH probably interfered 

 with the normal growth response at some stage before GA exerts its 

 effect. They interpreted Bukovac and Wittwer's experiments as well 

 as their own as showing that MH reduced or prevented the response 

 of GA-sensitive plants lo GA. GA does not reverse MH-induccd in- 

 hibition of cell division, yet the story may be quite different where cell 

 expansion is involved. For this reason it is still difficult to assess MH- 

 GA interactions in the over-all growth of plants. 



