Plant Qrowth'Suhstances 



The crux of the preparation Ues in the apparently simple 

 recommendation to germinate the peas on a damp material. 

 Germination is easy to accomplish, but peas are very prone 

 to invasion by micro-organisms, often borne on the seeds 

 themselves, and unless suitable treatment is applied, the 

 experimenter is liable to the disappointment of finding the 

 seedlings as a pulpy, stinking, mass. It is hoped that the follow- 

 ing suggestions will anticipate for once the reproach that text- 

 books give all the details except the essential ones. 



The pea seeds (Alaska) should be externally sterilized. 

 This may be accomplished by shaking the peas in any easily- 

 removable disinfectant, such as free chlorine, or by washing 

 in 95 per cent, alcohol followed by 0*2 per cent, aqueous 

 mercuric chloride solution (not in reverse order !). A simple 

 and effective method is to cover the peas with concentrated 

 sulphuric acid (pure oil of vitriol), and leave them in it for 

 five minutes with occasional shaking. A conical flask of large 

 capacity is best. Whatever method of sterilization is adopted, 

 rinsing should be performed with several changes of water. 

 Tap water will do, as absolute sterility is not necessary. If the 

 sulphuric acid method is used, the first addition of water to 

 the peas should be made rapidly and in great excess, with 

 avoidance of local overheating (for the sake of the peas), and of 

 spurting (for the sake of the operator). 



Sand is perhaps more conveniently freed from unwanted 

 organisms than are cloth and paper, which are best sterilized 

 by autoclaving or baking. Heat-sterilization of large amounts 

 of sand is a tedious process of uncertain effect. A sufficient 

 degree of freedom from micro-organisms can be attained by 

 the use of strong chemicals, such as are available to many 

 workers not possessing an autoclave. Here again, any reason- 

 able method can be adopted. The following technique gives 

 satisfactory results: 



Sand q.s. is placed in a stout-walled shallow vessel. Better 

 than the usual laboratory ware, a glazed "china" pie-dish 

 fills all requirements. The sand is treated with a hot solution 

 of potassium permanganate acidified with sulphuric acid 

 (5 or more grams per litre of each substance, and 60° C.) and 



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