ROOT-KNOT DISEASE OF TOMATOS. 



33 



ioo feet long, with beds 2\ feet wide on either side. These beds 

 were raised above the ground level, the top level of the growing soil 

 being about 18 inches above the floor level, and the subsoil of the 

 beds about 9 inches above the floor level. To insure a healthy crop 

 the grower put in virgin soil every year, but he found that the 

 infection remained in the subsoil, and year after year the tomatos 

 at certain marked places were invariably " clubbed." 



These infected places became more extensive each year, and when 

 the soil was being taken out particles of infected soil were carried or 

 brushed to other places so that the number of " club " areas increased 

 in this way also. On several occasions he had the subsoil dug out 

 at such places and a fresh subsoil put in. In every case he found, 

 however, that after the lapse of one year or two the disease reappeared 

 at the same places, so this plan was abandoned. His difficulty therefore 

 lay in the subsoil and the containing walls, and on consideration of 

 the matter it appeared reasonable and safe to treat these subsoils 

 with substances which it would perhaps be rather rash to use in the 

 actual growing soil. 



It was therefore assumed at the commencement of the experiment 

 that : 



1. The substances used would probably inhibit the development 

 of the eelworms or kill them outright. 



2. The roots of the tomatos would not grow down into the subsoil 

 if the substances therein were noxious. 



3. That the noxious substances would gradually descend because 

 of the watering of the tomatos during the growing season. 



4. That, as the substances gradually descended, a poison-stratum 

 (more or less) would prevent the ascent of the worms and the latter 

 would either be killed in this way or at any rate be kept from the 

 plants. 



5. That the tomatos had plenty of soil room and nourishment 

 in the top layer of soil and need not descend into the subsoil. 



Preparatory Work. 



In the season 19 14 the tomato crop had been followed by a 

 cucumber crop, which had suffered in some of the houses from certain 

 fungus diseases. As a precaution against a repetition of this in 

 1915, the subsoil and pathways were watered with a solution of copper 

 sulphate, 6 lb. to 60 gallons of water to 2 square rods of subsoil. 

 The glass, woodwork, and walls were sprayed all over with dilute 

 formaldehyde, 2 pints of commercial formaldehyde to 30 gallons of 

 water. After spraying, the doors and ventilators of each house 

 were closed and remained so till the fumes of formaldehyde could no 

 longer be smelt. 



After this the subsoil, where diseased, was forked over 3 inches 

 deep and treated further as described later on. 



VOL. XLIV. D 



