47 



the plants they were always watered with filtered water. Hence all 

 source of contamination was eliminated. Result, 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. 

 Instead of the soil in the pots all being heated to 212*^ F. they 

 received the following various degrees of heat before planting : 



No. of pot, I 2 3 4 5 6 7 S 9 10 II 12 



Temperature, 114° 118° 127° 140° 147° 150° 159° 161° 163° 163° 170° 176° F. 



Result. Nos. 1,2, and 3 all damped' off. The remainder were 

 perfectly free from the damping fungus and nematodes. 



Exp. d. Sixteen pots of cucumbers treated the same as "c." 



No. of pot, I 2 3 4 5 6 7 S 9 10 II 12 13 14 15 16 



Temperature, 147° 149° 154° 159° 163° 167° 168° 172° 176° 183° 185° i8&° 192° 194° 196° I99°F. 



Result, no nematodes. 



From these experiments which only represent about one-half of 

 what was clone it appears that a very high temperature is not neces- 

 sary in order to free infested soil of nematodes. The number of 

 degrees of heat necessary is about 140"^ F., but as a matter of safety 

 the temperature should go above this inasmuch as in large areas of 

 soil the distribution of heat is always unequal, and while one portion 

 may be heated as high as 190° F. another portion may not exceed 

 110° F. The conclusion then that the soil must be heated under 

 pressure to a temperature of 225'* or 235° F. in order to kill all 

 nematode life is therefore not valid in all cases. These experiments 

 were made with sufficient care and were repeated often enough with 

 the same results to consider them trustworthy. The practice of 

 soaking the seed in a strong solution of corrosive sublimate before 

 planting them was perhaps an unnecessary precaution inasmuch as 

 we have never been able in repeated examinations to find any evi- 

 dence of nematode infection from this source, but the watering of 

 the pots with filtered water- or water which had been previously 

 boiled was quite necessary where we were making observations upon 

 non parasitic species. We have observed many instances of steril- 

 ized soil becoming infested with the non parasitic nematodes from 



1. The damping fungus in this case was the Pythium De Baryanum, Hesse, which is 

 frequently troublesome to cucumber seedlings. 



2. We used for this purpose an ordinary sand filter which we attached to the faucet. 



