THE GROWTH OF HIGHER PLANTS IN SOILS FREE OF 

 MICROORGANISMS.* 



By E. B. FRED. 



{From the Laboratory of Agricultural Bacteriology of the University of Wisconsin, 



Madison.) 



(Received for publication, March 20, 1919.) 



In a study of the action of bacteria in soil it is frequently desira- 

 ble to determine the relation that exists between the microorgan- 

 isms and higher plants. The procedure is comparatively simple if 

 small plants or seedlings are used. For this purpose test-tubes, 

 especially the large Pyrex tubes described by Knudson/ give excel- 

 lent results. Where it is necessary to grow large plants and to carry 

 these to maturity, the procedure is not so simple. On account of the 

 size of the apparatus and the length of time required for the develop- 

 ment of large plants, it is difi&cult to prevent contamination. Some 

 of the points which deserve special care are: (1) sterilization of the 

 apparatus, of the medium, and of the seed; (2) planting of the bacteria- 

 free seed or seedling; (3) adding the sterilized water required for 

 plant growth. 



The nature of the medium used for the plants determines the time 

 of sterilization. If a synthetic medium, liquid or soHd, is used it 

 rarely requires a long period for sterilization. Soil, however, is ex- 

 tremely difiicult to sterilize and in order to kill all the bacterial spores 

 that may be present it is necessary to heat it for a long time and at a 

 high temperature. 



The destruction of bacteria on the seed-coats is in the majority of 

 cases readily effected by means of mercuric chloride solution in a 

 partial vacuum. Although a great number of methods have been 

 recommended for the sterilization of seed, I have uniformly secured 



* Published with the permission of the Director of the Wisconsin Agricultural 

 Experiment Station. 



^ Knudson, L., Cornell Univ. Agric. Exp. Station, Mem. 9, 1916, 17. 



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