122 EXPERIMENT STATION. [Jan. 



deficieut in this respect may cause injury to the crop when ster- 

 ilized. 



We have nuiintained that the benefits resulting from soil ster- 

 ilization are largely chemical in nature, as shown by experiments 

 with seeds, etc. In two series of experiments/ in which a large 

 number and several varieties of seeds were em})loyed, we found 

 not only a marked acceleration in germination, but considerable 

 increase in the number of seeds that germinated in sterilized soil 

 when comijared with the same soil unsterilized. The stimulating 

 effects produced in these tests were undoubtedly chemical in 

 nature; that is, there were certain substances in the soil which 

 were chemically changed by the process of steaming, and these 

 being absorbed by the seed, increased germination followed. It 

 is, however, not at all improbable that part of the stimulating 

 effects on seeds grown in sterilized soils is due to the renovation 

 of the gases contained in the soil, since the old gases are driven 

 out by the process of steaming. Steaming, in other words, has 

 to a certain extent the same effect as aerating the soil, which 

 process greatly stimulates seed germination and growth. In one 

 experiment where 3,000 lettuce seed were grown in two boxes, 

 1,500 in each box and one being aerated and the other not, it was 

 found that 86 per cent, germinated in the aerated soil, while 

 only 64 per cent, germinated in the unaerated soil. The average 

 weight of seedlings was 46 per cent, greater in the aerated than 

 in the unaerated soil.- 



Our experiments ^ in germinating seeds in decoctions of ster- 

 ilized soil showed that the decoctions exerted a chemical stimula- 

 tion, and that even decoctions from unsterilized loam had a 

 similar effect on germination. The soil we used had never re- 

 ceived any commercial fertilizer, but was a typical market- 

 garden soil, frequently enriched with decomposed horse manure. 

 It is well known that a great variety of chemicals stimulate seed 

 germination, and it is not surprising that decoctions of soils 

 would do the same. 



The increase in the number of bacteria in sterilized soil has 



' Hatch Exp. Sta., 15th Ann. Rept., 1903, p. 41; also Hatch Exp. Sta., 18th Ann. Rept., 1006, 

 p. 126. 



' Hatch Exp. Sta., 18th Ann. Rept., 1906, p. 124. 

 > Hatch Exp. Sta.., 18th Ann. Rept., 1906, p. 129. 



