23 



practically the whole amount of soil became desiccated. The result 

 of drying out the soil in one bed containing 308 plants can be seen 

 in Diagram V, which shows the same bed and soil used in the pre- 

 ceding experiment, literally covered with diseased lettuce plants, 

 representing in this case the Drop and Rhizoctonia. The number 

 of plants which succumbed to the two diseases is 301 out of a total 

 of 308, or 97%. The number subject to Drop was 235 or 76% and 

 the Rhizoctonia gave 66 or 21'/^. 



The other half of the house with the bed containing 264 plants 

 waa-treated similarly, with about the same results. The increase in 

 the Drop due to drying was 64% over that of the same soil in the 

 preceding experiment (Diagram IV), which shows that this method 

 of treatment cannot be recommended. It is undoubtedly the influ- 

 ence of desiccation upon the sclerotia that accounts for the remark- 

 able loss from Drop which some growers have experienced. 

 a b n 



• =Drop 



©— TRhizoctonia 



Diagram \'I. n. untreated plot, a, treated with hot water from the boiler; tem- 

 perature of water 210° F. b, treated with steam cultivator. 



The experiment shown in Diagram VI followed the pre- 

 ceding one and some other methods of control were tried, such 

 for example as covering the surface of the soil with one inch of saw- 

 dust, packing two inches of excelsior around the plants and over the 

 soil,* allowing the plants to grow through 2 in. meshes of wire net- 

 ting raised 2 or 3 inches above the bed in order to keep the lower 

 leaves from touching the soil, heating the top layers of soil with -hot 

 water, and an application of steam to the surface of the soil by 

 means of an improvised steam rake or cultivator. The steam culti- 



•As recommended by Garman. 



