I 



ELISHA MITCHELL SCIENTIFIC SOCIETY. 123 



111 knots partly eaten by insects, which is quite common, the 

 masses of bacteroids become surrounded anew by a membrane 

 and the bacteria-tube thus formed by sprouting divides into 

 successively smaller colonies surrounded by membranes, which 

 Prazmowski first took to be a kind of spore formation when the 

 real nature of the organisms were unknown to him. 



The structure of the knot is adapted to favor the symbiotic 

 relation which exists between the host plant and its parasite. 

 The corky layer of the rind prevents not only the ingress of 

 foreign organisms, but prevents the escape of the bacteroids, 

 while the fibrovascular tissue which surrounds the bacteroid tis- 

 sue provides the channel of communication between the plant 

 and the contents of the knot. The plant being the master 

 imprisons the bacteroids within the tissues of the knot, for a 

 time nourishes them with the material which is the product of 

 carbon assimilation in the leaf and the willing bacteroid slave 

 assimilates atmospheric nitrogen producing protein matter, when 

 finally the plant completely overpowers them, dissolves their 

 bodies and carries off their protein contents for its own use. 



yii. 



TREATMENT. 



The following discussion of the treatment of the root-gall 

 nematode is mainly suggestive, and anything farther must be 

 preceded by careful experimentation. 



Difficulty of Remedial Applications to Plants 

 Already Diseased. — It is evident from the endoparasitic 

 habit of the worms that direct applications of vermicides to 

 the roots will not destroy them without fatally injuring the 

 plants themselves. When the worms first enter the tissues 

 of the roots they are so minute that no channel is left large 

 enough for the entrance of any poisonous fumes which 

 might be applied in the soil. Also the hypertrojihy of the 

 tissue of the roots incident upon the presence of the parasites 

 would effectually close up any aperture made. Dr. Neal,* 



*Bulletin 20, U. S. Dept. Agr. Division of Entomology. 



