SOIL STERILIZATION 87 
which is considered the most serious of the animal foes, 
is repressed both in the egg and worm state by thorough 
steaming. Weed seeds are. also destroyed and plant 
food is made more available. Several investigators have 
shown that steam sterilization increases the amount of 
soluble or available nitrogen, potash and phosphoric 
acid. It also increases the absorptive power of the soil 
for water. Some of the experiments indicate that steam 
sterilization tends to develop certain toxics and also in- 
creases the acidity of the soil.. If lime, however, is 
applied before the soil is sterilized, there need be no fear 
of any harmful effect. 
In this connection, Stone and Smith state the follow- 
ing in Bulletin 55 of the Massachusetts station: “In the 
numerous crops of cucumbers, tomatoes and lettuce 
which we have grown in sterilized earth we have never 
noticed anything 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 cultures of sterilized and unsterilized soil and 
have invariably noticed these effects on cucumbers and 
lettuce.” 
Rudd, whom we have already quoted as having tried 
the sterilized method, says :* 
“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 physiol- 
ogists that the presence of humus in the soil plays an important 
part in the 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 has been subjected to the action of steam for several hours 
* American Florist, Vol. IX, p. 171-197. 
