Physiological and Anatomical Effects 1 1 5 



per cent and this stimulation continued for at least 5 successive inter- 

 nodes. Tests of auxin activity of these extracts were not made with 

 any standard assay procedures. There appears the inviting possibility 

 that the hormones extracted were stabilized against normal auxin- 

 destroying systems in the plant and hence could continue their stimu- 

 lative effects over a long period of time. 



Another overall stimulation of growth by auxin applications to 

 intact plants has been achieved by means of the short-time application 

 of auxins to seeds. Experiments in which seeds are germinated in 

 auxin solutions and permitted to remain in them nearly always re- 



100 mg/l 



CONC. OF AUXIN 



Fig. 52. Effects of the soaking of oat seeds with various concentrations of indole- 

 acetic acid on later growth. The data on root length taken after six days; the dry 

 weight and height after maturity (from Thimann and Lane, 19.S8). 



suit in gross inhibitions of growth and development. However, short- 

 time treatments of seeds in auxin solution have frequently given 

 very considerable gains in subsequent growth rate of both shoots and 

 roots. A graphic case is the report of Thimann and Lane (1938). They 

 soaked oat seeds for 24 hours in indoleacetic acid solutions, and ob- 

 tained 30 to 60 per cent increases in subsequent root length, plant 

 height and final plant weight (figure 52). The auxin treatments of 

 seeds yielded earlier and more abundant flowering. The possibility of 

 using this type of treatment to obtain greater growth in crop plants 

 has led to many attempts of this sort. However, it seems that gains in 



