NEMATODA ANGUILLULIDAE 



155 



Yon Linstow l has pointed out that the free form of A. 

 diplogaster, if found alone, would be placed in the genus Diplo- 

 y aster; similarly the bisexual form of Ascaris nigrovenosa is known 

 as Rhabditis nigrovenosa. 



Those Nematodes which live parasitically in plants, e.g. many 

 of the genera Tylenchus and Aphelenchus and Heterodera, as 

 well as those which only pierce the epidermis of the roots (the 

 remaining species of the above-named genera), are provided with 

 a spine which works to and fro through the mouth and assists the 

 animal to bore into the tissues of the plant. Tylenchus devastatrix 

 lives and reproduces in leaves and stems (never in the roots, 

 except in the case of hops 2 ) of many cultivated plants, such as 

 rye, oats, onions, etc. " Clover sickness " is probably caused by 

 this Nematode. The plants become infected by the thread- 

 worms in the soil during the spring ; their presence causes swell- 

 ings and often kills the plant, in which case the worms return to 

 the soil or remain in the straw. 



Tylenchus tritici Need, is the cause of " ear-cockles " in corn. 

 These take the form of brown 

 or purple galls, which replace 

 the grains of corn, and which 

 contain hundreds of minute 

 Nematodes. In these galls 

 they are motionless, and are 

 capable of surviving in dry- 

 ness for at least twenty years ; 

 but when moistened, for in- 

 stance, by the gall falling on 

 damp earth, they resume 



their vitality and make their FIG. 77. A, , Female Heterodera schachtii 

 " Schmidt, breaking through the epidermis of 



way to the young wheat 

 plants, and then, wriggling 

 up the leaves and stems, 

 find their way to the ear. 

 Here they pair, and produc- 

 ing a gall-like growth in the flower, lay numerous eggs, from 

 which arise the Nematodes of the ear-cockle. 



Heterodera schachtii 8 Schmidt, is the cause of the " beet sick 



1 Centrbl. Bakter. vol. viii. 1890, p. 489. 2 J. Percival, Nat. Sci. voL vi. 1895, p. 187. 

 3 A. Strubell, Bill. Zool. Bd. i. Heft 2, 1888, p. 1. 



a root ; the head is still embedded in the 

 parenchyma of the root : B, a, larvae boring 

 their way into a root ; b, larva of the immobile 

 kind surrounded by the old skin, living as 

 an ectoparasite on the outside of the root. 

 (From Strubell.) 



