CHAPTER VI 



THE TREATMENT OF SEEDS 



In 1937 Grace suggested that if young lettuce, tomato, and 

 other seedlings growing in sand or soil are treated with a solu- 

 tion containing indole-acetic acid or other synthetic growth- 

 substance, a real stimulation is obtained with a dose of active 

 substance at the rate of 50 to 250 mg. per acre (120 to 600 mg. 

 per hectare). This is, so far, the ultimate in agricultural micro- 

 therapy, and, should active substances be present in organic 

 manures in only corresponding traces, their detection will 

 provide a problem for the analyst. A pictorial height-curve 

 of nasturtiums treated with such minute doses has been 

 provided by Grace in two publications (1937, 1938 a). 



Grace (1937) has also proposed two dusting techniques 

 which could be used not only for cuttings but also for seeds. 



An inert dust such as talc, or a standard mercurial dust 

 disinfectant such as is used for cereals, had a small proportion 

 of indole-acetic, indole-butyric, or a-naphthyl acetic acid 

 mixed with it. Grace claimed that treatment with such dusts 

 is safer than treatment with solutions. A toxic excess of 

 growth-substance can be easily avoided in the solution treat- 

 ment of such relatively massive material as cuttings. In the 

 case of seeds, which are not only small but may be supposed 

 while germinating to have little need of auxin-like material, it 

 is very easy to give a toxic overdose of artificial growth-sub- 

 stance — as, indeed, the work of Grace has shown. Some toxic 

 effects of solutions applied to seedlings are discussed in 

 Chapter XI. 



The dust technique appears to be peculiarly suitable for the 

 treatment of seed with artificial growth-substances. Grace 

 treated seeds of wheat, barley, and other plants, with a dust 



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