WORMS. 229 



outside (Fig. 134, 1). The entire development from 

 egg to sexual adult takes four or five weeks, and 

 there may be six or seven successive generations, the 

 reproduction is consequently very rapid. 



It also obviously follows that " beet sickness " of 

 the soil is especially prevalent in fields where there 

 has been an excessive amount of beet culture. The 

 disease, however, may suddenly appear in fields which 

 have been hitherto " safe " for beet, and in many such 

 cases it has been proved to result from manuring with 

 artificial compost rich in refuse from afiected fields. 

 The disease frequently appears, too, in fields where 

 beet have never been cultivated, but where cabbage 

 has been grown for a long time. It has been shown, 

 especially by Kiihn's investigations, that the beet 

 eelworm can live in many plants both cultivated 

 and wild, e.g. of the former, cabbage, rape, mustard, 

 garden cress, chickling peas, mangold, oats; of the 

 latter, charlock, spurrey, couch grass. These researches 

 are of the greatest importance both for understand- 

 ing the way in which beet sickness spreads and in 

 combating it. 



Preventive Measv/res : Manufactured compost must 

 not be used as a manure on beet-fields. The refuse 

 from infested beets, if used on other fields, must be 

 mixed with one-sixth its bulk of quicklime. The 

 boots of labourers employed in beet-sick fields, the 

 hoofs of horses working in them, and also the imple- 

 ments used, must be carefully cleansed lest infected 

 earth should be carried to other fields. Bemedies: 

 Kiihn has recommended the use of plants which 

 attract the eelworms (" lure-plants "). He sows on 

 beet-sick land rapidly germinating plants, of kinds 

 which the worms readily attack, and weeds them out 

 again when they have become infested by the para- 

 sites, but before these have had time to mature and 

 re-enter the soil. The eelworms are thus allured into 

 the plants grown, and destroyed with them. Such 



