5 o2 SCIENCE PROGRESS 



in contact with water during ten days. This oiliness is notice- 

 able, in many cases, in grassed soil, though to a less extent than 

 in heated soils: of fourteen pairs of different samples of soil, 

 one being taken from under grass and the other from tilled 

 ground immediately adjoining, eight showed that the grassed 

 soil was less readily wetted than the tilled soil. 



The attempts made to discover a toxic action affecting the 

 germination of seeds in soil from grassed land have been un- 

 successful; they showed that there was a small, though undoubted, 

 difference between the action of such soil and of soil from tilled 

 ground but in the opposite direction, the grassed soil being the 

 more favourable. In view of the readiness with which a small 

 proportion of the toxin will oxidise and produce favourable 

 results, this is not inconsistent with some toxin having been 

 present when the samples were taken ; but it cannot be used as 

 an argument that such was the case. The fact, however, that 

 there is some difference in action, whatever the direction 

 may be, is more favourable to such a view than if there were 

 no difference. 



The increase of fertility produced by heating soil and by 

 treating it with antiseptics, has recently been put to practical 

 use in the case of soil used in greenhouses and hothouses and 

 an explanation of the result, differing from that detailed above, 

 has been given. According to the work of Russell and Hutchin- 

 son, when soil is heated to 50 or is treated with antiseptics, the 

 greater number of the bacteria present and all the protozoa 

 which feed on bacteria are killed, the result being that the 

 surviving bacteria are able to multiply without check and soon 

 outnumber those present in unheated soil and by this action a 

 corresponding increase in the supply of nitrogen available for 

 plant growth is brought about. 



Without in any way controverting the evidence on which 

 this view rests, it seems impossible to accept it as the only 

 or even the principal explanation of the behaviour of plants 

 in heated soil. According to it, a maximum of fertility should be 

 observed in the case of soil heated to 50 , corresponding with the 

 temperature at which all the protozoa are killed and the injury 

 to the bacteria is incomplete : as the temperature of heating 

 is raised, the fertility should decrease or at any rate should take 

 longer to make its appearance, as a larger number of the 

 bacteria would have been killed ; and in the case of soils heated to 



