Stem Eelworm, 



471 



of Tylenchus devastatrix were found in them. There were 

 other species of eelworms present, especially that known as 

 Heterodera Schadii^ which was seen in abundance upon 

 the smaller roots. 



Some grasses are attacked by Tylenchus devastatrix, 

 notably, Anthoxanthum odoratuin, Holcus lanatits, and Poa 

 anmta. Weeds are also infested by it, as the daisy, common 

 shepherd's purse, spurrey, buttercup, cornflower, sow 

 thistle, and others. 



The full-grown eelworm [Tylenchus devastatrix) is about 

 the twenty-fifth of an inch long. Its length varies some- 

 what in different root plants. In appearance it resembles a 

 tiny eel, with both ends sharply pointed. It has, in common 

 with other species of Tylenchus , a sharp spear-shaped point 

 within the gullet, which has been well described as an 

 exertile spear on a trilobed base," serving to pierce the 

 tissue of the root plants and to extract their juices. The 

 eggs are oval, and sometimes oblong in shape, as shown 

 in the figure, and are found in the tissues of the 

 host-plants, together with larvae and fully developed eel- 

 worms. The growth and progress of the larva can be seen 

 in various stages within the transparent eggs. When the 

 larvse come from the eggs. Dr. Ritzema Bos says, they are 

 about one-seventh of the size of the adult eelworm, and 

 resemble them in outward appearance, though their internal 

 parts differ somewhat. The larva undergoes several changes, 

 or moults, before it becomes a perfect eelworm. Close 

 examination of the habits of the Tylenchus devastatrix indi- 

 cates that it lives and feeds in living tissues. When the 

 tissues of the host-plant decay or die, the eelworms and 

 larvse either fall to the ground and enter it, or the larvse and 

 the eggs remain in the decaying and dead parts, and become 

 dried up with them. The larvae have the power of resuming 

 animation and active life after they have remained in a 

 perfectly dry condition, in dead tissues, or in dry soil, even 

 for several years. The eggs also can regain vitality after 

 animation has been suspended for two to six months, accord- 

 ing to their condition when the period of suspension 

 commenced. Dr. Ritzema Bos revivified larvae which had 



