SOIL STERILIZATION 89 



Steam Sterilization 



Temperature required. Definite information gained 

 from experiments relating to this question is contained in 

 Bulletin 55 of the Massachusetts station, from which is 

 quoted the following : 



"Our experiments upon this point were numerous, and they were 

 made with earth containing abundance of nematodes of various 

 species in all stages of development. For the sake of convenience 

 we will designate these experiments as a, b, c, etc. In all of these 

 experiments we employed cucumbers in pots of various sizes (from 

 4 inches to 10 inches), and the plants were left until they were 

 sufficiently large to show root galls upon them if nematodes were 

 present in the soil. In every case except 'a' the pots containing the 

 infested earth were sterilized in an Arnold steam sterilizer, and 

 when moderate heating was required they remained in the sterilizer 

 only a few minutes. 



"The earth in experiment 'a' was part of a large lot which was 

 sterilized in a box by means of steam from a boiler. In every in- 

 stance numerous microscopic examinations were made of the soil 

 and roots of the plant in order to determine whether nematodes 

 were present. The non-parasitic species are generally present in al- 

 most every soil, and their presence can very often be suspected by 

 the coloration of the root. They are generally found on the older 

 parts of the root near the surface of the soil, as indicated by the 

 dirty brown color of the epidermal tissue. The experiments are as 

 follows : 



"Exp. a. Six 4-inch pots were filled with infested earth which had 

 been heated to 212 degrees. The pots were also sterilized and the 

 cucumber seeds after soaking 12 hours in water were placed for 

 10 minutes in a saturated solution of corrosive sublimate, and be- 

 fore using were rinsed with sterilized water. During germination 

 and the growth of the plants they were always watered with filtered 

 water. Hence all source of contamination was eliminated. Results, 

 no nematodes. 



"Exp. b. Six plants treated as above. Result, no nematodes. 



"Exp. c. Twelve pots of cucumbers, the seeds of which were 

 treated as in Exp. 'a' and the plants watered with sterilized water. 



