58 



heated in two hours, and according to Mr. May he heats 112 cu, ft. 

 in one and one-half hours. 



Effects of Heating the Soil on the Growth of the Crop. 



In the numerous crops of cucumbers, tomatoes, and lettuce which 

 we have grown in sterilized earth we have never noticed any thing 

 of a detrimental nature, but on the other hand a decidedly beneficial 

 effect as the result of sterilization. Not only is this shown in the 

 difference in color which the plants take on, but in an appreciable 

 acceleration of their growth. We have repeatedly run parallel cul- 

 tures of sterilized and un sterilized soil and have invariably noticed 

 these effects on cucumbers and lettuce. Mr. W. N. Rudd whom we 

 have already quoted as having tried the sterilizing method says as 

 follows': — " One would imagine that the cooking would make the 

 soil soggy, but it has no such effect, and indeed the soil seems in 

 better condition afterwards than before the steam was applied, and 

 the fine condition of the plants growing in soil which has been 

 treated proves that the soil has not been injured in the least." It 

 has long been known among practical gardeners that heating the 

 soil produces beneficial results. Every greenhouse soil contains 

 humus or vegetable mold and it is recognized by vegetable physiolo- 

 gists that the presence of humus in the soil plays an important part in 

 assimilation and plant growth, but its efficiency depends partly upon 

 the stage of decomposition at which it has arrived. It has been 

 shown by experiments in which plants are treated in one case with 

 humus in the raw condition, and in the other with humus which had 

 been subjected to the action of steam for several hours at a temper- 

 ature of 212^^ F., that there is considerable difference in the yield of 

 the crop. It has been found that the same quantity of soil, after the 

 action of heat, yields a crop many times in excess of the former or 

 untreated soil. In other words by heating we convert the humus 

 compounds in the soil into a more available form for the utilization 

 of the plant. That the heating of the soil gives rise to some changes 

 is shown by its darker color and more porous condition, and it is 

 undoubtedly due to these changes which have taken place in the 

 humus compounds which account for the accelerated and vigorous 

 growth of the plants. Another feature which is characteristic of 

 sterilized soils is the unusual occurrence of humus loving plants, or 



I American Florist, Vol. IX, p. 171-197. 



