CONTROL OF DAM PING-OFF 17 



soil already ^reed of soil fungi, formaldehyde was applied immediately altei 

 seeding, to previously untreated soil and to soil which had been steamed five 

 days earlier. 



As may be seen in Table 16, formaldehyde improved the growth cf all veg- 

 etables in soil not previously treated and, except with lettuce, steaming had a 

 similar effect. But in no case did formaldehyde applied to steamed soil ''mprove 

 the growth of plants as compared with their growth in soil which was steamed 

 and received no formaldehyde. It seems probable that the stimulatory effect of 

 formaldehyde is due principally or wholly to its freeing the plants of the retarding 

 effect of soil fungi. It is noteworthy, too, that formaldehyde when applied to 

 steamed soil often interfered with growth although it had quite the opposite 

 eflfect on soil not steamed. There is not much likelihood of formaldehyde's being 

 applied tc soil recently steamed; but if, for any reason, it is, the results may 

 apparently be unfortunate. 



Table 16. — Effect of Formaldehyde, in Steamed and Unsteamed Soil, 

 ON Green Weight of Plants 



To learn how many times it is safe to water with very dilute formaldehyde 

 (4.9 cc, one teaspoonful, in 2 gallons water) after seeding, and to learn how this 

 controls damping-off, soil was treated at the time cf seeding and again once or 

 twice mere at intervals of 2 days. Results are recorded in Table 17. 



Table 17. — Effect of Dilute Formaldehyde Applied to Soil More Than 

 Once After Seeding 



Number of Relative Number of Percentages Relative Green Weight 



Treatments Plants Which Lived Which Damped-ofif per Plant 



with ■ — 



Formaldehyde' 



Beet Cress Cucumber Beet Cress Cucumber Beet Cress Cucumber 



None (check) 100 100 ICO 30 11 12 100 100 lOO 



One 323 233 131 2 121 143 141 



Two 326 158 124 10 135 114 105 



Three 292 141 122 3 114 86 74 



'One teaspoonful in 2 gallons water. 



Three applications did not injure growth of beet (nor, in another experiment^ 

 growth ot pepper) but three applications retarded the growth of cucumber and 

 cress seedlings. Growth of all was improved or unaffected by two applications, 

 but the number of plants which lived was. in all cases, increased as much by one 

 application as by more. It is of interest to note that, although 0.5 teaspoonful 

 formaldehyde per gallon (and about 1 quart of the solution per square foot) gave 



