ELISHA MITCHELL SCIENTIFIC SOCIETY. 125 



thorough investigations must be made to determine the useful 

 plants which are very nearly or quite insusceptible to the attacks 

 of the worms. By growing such crops upon selected ground 

 for a ])eri()d of a few years, exercising at the same time great 

 caution in not allowing any weeds or grasses, which may be sus- 

 ceptible, to grow, the area selected could be sterilized. Now by 

 taking up successively different areas and treating them in the 

 same manner a persevering farmer could practically rid his land 

 of the worms. So far as observed here buckwheat and alfalfa 

 are among the insusceptible plants which could be experimented 

 with. 



Rotation of Crops. — Here w^e find occasion again to empha- 

 size the oft- repeated necessity of a judicious rotation of crops, 

 but with special reference to a wise alternation of insusceptible 

 with susceptible plants. It is evident that if we start with a 

 sterilized soil and grow for one year an annual which is liable to 

 the disease there is little danger of infection of the ground. If 

 the following year this is followed up by the cultivation of 

 another nearly or quite free from attack the soil will with greater 

 safety bear another crop of the plant grown the previous year. 



Clean Cultivation. — The absence of clean cultivation is 

 one of the most fruitful sources of the thorough impregnation of 

 the soil w^ith the worms. It was, of course, impossible to make 

 an application of this principle to the enemy in question before 

 that enemy was known, and especially before the time required 

 for its complete development from the egg had been determined. 

 Now that these facts are known, and since we know many of the 

 plants subject to the disease, it is to be Imped this method will 

 be employed by those desirous of subduing the worms. Not 

 only should an effort be made to prevent the growth on arable 

 land of all plants growing wild which are liable to serious infec- 

 tion, but so soon as a crop has been gatiiered, or it is found that 

 the crop will not be worth gathering, from any cultivated plant 

 liable to serious infection the farther growth of the plants should 

 be stopped, or, what is better, the roots of the plants should be 

 gathered and burned when possible. In gardens this would not 



11 



