EELWORMS 



559 



to the fact that the eelworms in the tissues of a fern frond 

 cannot extend beyond the portion of parenchyma circum- 

 scribed by a vein. According to Ritzema Bos, when the air 

 is moist the eelworms migrate from old diseased parts of the 

 leaf and enter the adjoining healthy portions, emerging and 

 entering through the stomata, and that when attacked plants 



FIG. 170. Aphelenchus olesistus. i, surtace view of 

 fragment offrond, showing eelworms under the surface 

 of the epidermis. It will be observed that the size of 

 the stomal opening is sufficiently large to admit the 

 passage of the eelworm ; highly mag. ; 2, Pteris droog- 

 mansiana ; 3, Adiantum capillus-veneris, form fissa ; 

 4, Lygodium volubile. In the last three figs, the dark 

 portions are caused by eelworms ; reduced. 



are placed in fairly dry air, the migration is checked. I have 

 never seen eggs in the tissues of infested plants, and imagine 

 that they are deposited in the soil in which the plant is 

 growing, the eelworms ascending the plants and entering the 

 tissues for feeding purposes only. I have found eelworms in 

 abundance in the soil in which infected plants were growing. 

 In addition to ferns, Aphelenchus lives in the leaves of many 



