EELWORMS 551 



' A pressure of steam exceeding 50 Ibs. is not only cheaper 

 but more effective than a pressure which falls below this, 

 and the amount and cross section area of the tile is im- 

 portant. The cost of heating soil depends upon the equip- 

 ment employed and cost of labour, etc. Probably not far 

 from 100 cu. ft. of soil under the most favourable conditions 

 can be heated in one hour's time to a temperature of over 

 200 F. 



'The minimum amount of heat necessary to kill nematodes 

 and their eggs while confined to the soil is about 140 F., 

 but for all practical purposes it is desirable to make use of a 

 higher temperature, at least from 180-212 F. 



' The benefit of steaming and sterilising the soil is not alone 

 confined to the destruction of nematodes. Many other 

 greenhouse pests are killed. The mechanical conditions of 

 the soil are moreover greatly improved, the humus com- 

 pounds are rendered more available for plant food, which 

 results in giving plants grown in sterilised soil a considerable 

 acceleration in their rate of growth. 



{ The changes of the environment which appear to affect 

 Heterodera the most are freezing and dessication. Either 

 of these agencies might be employed in certain cases to kill 

 nematodes. The latter gives promise of becoming a cheap 

 and efficient method.' 



Sulphate of potash up to 3 cwt. per acre is recommended 

 where eelworms are present in fields, as in the case of 

 tulip-rooted oats, clover sickness, beetroot disease, etc. 



Stone, G. E., and Smith, R. E., Hatch Expt. Sta., Mass. 

 Agric. Coll., Bull. No. 55. 



Eelworms attack many different kinds of plants. Kiihn 

 gives a list of 180 European plants belonging to fifty-three 

 different families. This was in 1881, since which time the 

 list has been greatly extended. 



Eoot-knot disease in cucumbers and tomatoes (Heterodera 

 radicicold] often seriously injures cucumbers and tomatoes 

 by forming numerous knots or swellings on the root. 

 These galls vary in size from that of a turnip seed to 

 a marble, and are sometimes roughly globose, at others 

 elongated. The general structure of the root is much 

 modified by the action of the eelworms, and its power 

 of conducting water is materially checked, consequently 

 when the galls are present in abundance the root ceases 



