f 



8 BULLETIN 818, U. S. DEPARTMEITT OF AGRICULTURE. 



1. Damping-off of both lettuce and tomato seedlings on February 

 5 was quite prevalent in the check and in the section receiving 8,500 

 c. c. of boiling water, while it was found only to a slight extent in 

 the 13,500 c. c. treated section and not at all in the 17,000 c. c. 

 treatment. 



2. The average percentages of netamode infection occurring on 

 lettuce and tomato plants grown in treated sections Nos. 1 to 3 and 

 check section No. 4 were as follows: 40, 20, 4, and 68. For Rhizoc- 

 tonia they were 80, 8, 7, and 100. These figures indicate control 

 of the pathogenes in proportion to the amount of the hot-water 

 applications. A comparison of healthy plants from the 17,000 c. c. 

 section with typical nematode and Rhizoctonia diseased plants, from 

 the check section is shown in Plate IV, figiure 1. 



3. In the case of both test crops, while the plants in the untreated 

 section, No. 4, were dwarfed and yellowed, in the treated sections 

 they were of larger size and greater vigor the larger the amount of hot 

 water applied. The stand in the check sections was greatly reduced. 

 These points are clearly brought out in Plate III, figure 2. 



EXPERIMENT SERIES II. 



In studying the results secured from the preliminary experiments 

 already presented, additional data were desired to answer certain 

 questions which arose, viz: How much of the vigor and increased 

 growth of the plants in treated soil was due to the physical and chem- 

 ical effects of the heating on the soil, and how much to the absence of 

 plant pathogenes ? What temperatures were secured in the soil by 

 the various treatments given and for what lengths of time were they 

 maintained ? 



To answer these questions and also to make our results the more 

 conclusive, on May 3 the entire series of experiments was repeated 

 with more checks and with such changes and additions as would give 

 the desired information. 



METHOD OF PROCEDURE. 



Two lots of soil were used in the 4 and 8 inch pot experiments, viz, 

 infested soil and presumably uninfested greenhouse soil. The in- 

 fested soil used was the nematode and fungus infested soil from the 

 previous bench experiment with the addition of infested soil from the 

 tomato bed used as a stock culture for nematodes. This was thor- 

 oughly mixed and sifted and was further infected with nematodes by 

 mixing with the soil in the pots badly nematode-diseased tomato 

 roots cut into small pieces. The greenhouse soil was from a fresh 

 mixture not yet used in greenhouse work and presumably free from 

 the parasites under consideration. 



