16 H. H. Whetzel and John M. Arthur 



The small proportion of blooming plants in these plots in 1923 is to be 

 attributed largely to weak bulbs and not to the disease. 



It will be noted that in all three of the steam-sterilized plots (2, 3, and 

 4) a nearly perfect stand was obtained (Plate VII) and the proportion of 

 diseased plants was approximately the same, 3 to 6 plants to the bed. 

 This indicates that half an hour's steaming is as effective as the longer 

 treatments. 



Plot 5, treated with formaldehyde solution, gave a stand of 49 plants, 

 of which 8 showed disease and all blossomed (Plate VIII). 



Plot 6, the other check plot, gave a stand of 41 plants out of 52 planted, 

 but of these 21 showed disease; 15 bloomed (Plate VIII). This plot had 

 never shown a high percentage of disease, due apparently to a tile drain 

 across it which tends to keep the soil drier than in the other plots. 



These results indicate clearly that the bulb-rot pathogene may be largely 

 eradicated and a good stand obtained by soil disinfection with formalin 

 at the rate of 1 to 1| pounds to 5 or 6 square feet of soil. The formalin 

 should be diluted in enough water to thoroughly wet down through 

 from 6 to 8 inches of loosely spaded soil. Pan steaming for from one-half 

 to one hour also is effective. 



In the control, or check, plots in the spring of 1923, a few plants, as 

 already pointed out, came through with no trace of disease. It appeared 

 possible that these individuals were resistant or immune to the pathogene. 

 In order to test this possibility, these plants were dug after maturity and 

 saved for planting in the contaminated soil in the experimental plots that 

 autumn. The bulbs were planted in two extra rows on either side of plot 

 6, one of the checks for the experiment of 1923-24. Practically every one 

 of these bulbs grew and produced flowers in the spring of 1924, and again 

 showed no trace of the disease. This indicates rather strongly that they 

 are resistant or immune. Thus a strong probability exists that resistant 

 or immune strains of tulip varieties may be obtained by the selection and 

 propagation of disease-free individuals from populations growing in 

 badly contaminated soil. 



