1 



6 BULLETIlSr 818, U. S. DEPARTMENT OF AGRICULTURE. 



DISCUSSION OF RESULTS. 



From a study of the data presented in Table I, relative to the two 

 sets of 4-inch pot treatments, the results are here summarized. 



1. As a result of submersion of the soil in boiling water for 2^, 5, 

 and 10 minutes, no infection by root-knot nematodes, Pythium, or 

 Rhizoctonia occurred in either set of pots except in one pot which 

 showed a small amount of Rhizoctonia root discoloration. As this 

 minor infection occurred in one of the pots to which diseased roots 

 were added and which received the 2i-minute submersion, it is quite 

 probable this was due to insufficient treatment. The plants in the 

 check pots showed 83 per cent affected by nematodes and 100 per 

 cent severely diseased by the fungous parasites. A comparison of 

 the typical appearance of roots from treated pots and those from 

 untreated check pots is shown in Plate I, figure 1. 



2. Normal germination occurred in aU treated pots, an average 

 of 42 plants per pot, while in the untreated pots the stand was re- 

 duced by the soil organisms to an average of 1 2 plants per pot. 



3. All treatments prevented damping-off in both sets of pots, as 

 was shown by the final examination, while in the untreated check 

 pots half of the seedlings died after the first germination count made 

 two weeks subsequent to planting. (PI. I, fig. 2.) 



4. Throughout the experiment the plants in the check pots showed 

 pronounced yellowing and stunting, reaching an average height of 

 only 3 inches at the time of the final examination, as compared to 

 an average height of 5 to 7 inches for the plants in treated soil, all of 

 which were vigorous and of a healthy green color. 



Certain facts evident from a study of that part of the data in Table 



1 pertaining to the two sets of 8-inch pot experiments are here pre- 

 sented. 



1. The 18 treated pots showed an average of 74 seedlings per pot 

 two weeks after planting, as compared with an average of 22 for the 

 two check pots, a reduction of 70 per cent in the stand. The typical 

 appearance of treated and untreated pots at this time is shown in 

 Plate II, figure 1. 



2. A slight amount of damping-off occurred in two of the six pots 

 receiving the 1,000 c. c. treatment, while none was noted in the 12 

 pots which received the larger amounts of boiling water. In the 

 check pots, however, almost 60 per cent of the seedlings damped-off 

 between the first germination count and the final notes. 



3. The plants in the check pots remained markedly stunted 

 throughout the experiment, attainmg a final average height of only 



2 inches, and were considerably yellowed and unhealthy in appear- 

 ance. The plants grown in pots receiving 1,000 c. c. of boiling water 

 reached a final height of 3 to 4 inches and were slightly yeUow in 

 color. The plants in all pots receiving the larger treatments grew 



