NEMATODE DISEASE OF WHEAT. 7 



produces a wrinkling, twisting, and rolling of the younger leaf 

 blades, as shown in Plate I, A and B. Small raised, rounded areas 

 may appear on the upper surface of such leaves, which lose their 

 normal green color, become yellow, wilt, and die. Very young leaves 

 sometimes, however, show conspicuously none of these symptoms. 

 Occasionally they contain light-colored swellings or galls, one or 

 more of which may be located along the midrib, on the leaf edge, 

 or between the two, and are misshapen by an unequal lateral de- 

 velopment. A conspicuous gall on the edge of a leaf is shown in 

 Plate II, A and i> , and apical swellings near the midrib of a young 

 leaf 16 days after artificial inoculation are depicted in Plate II, C. 

 By tearing apart these leaf galls several weeks after they have been 

 induced, the eelworms which cause them can be found in all stages 

 of development. 



When seedlings become more severely attacked than already in- 

 dicated, more pronounced evidence of abnormality appears. The 

 young leaves become so strongly infected within the older leaf 

 sheaths that instead of growing straight up normally they may be 

 forced through the latter, carrying along with them the young stem. 

 In this way stems sometimes are bent and induced to grow in an 

 almost horizontal direction. The leaves become so wrinkled, twisted, 

 and rolled as to lose all semblance of their natural shape. Their 

 normal green color then disappears and finally, after wilting, the en- 

 tire plant dies. Diseased leaves sometimes roll so tightly as to hold 

 firmly the tip of the younger leaves. This results later in wrinkling 

 and more or less telescoping of these leaves as they grow from below. 



Leaf and stem symptoms of the disease occur more commonly on 

 the seedlings than on the older plants, which leads to the general 

 belief that the former outgrow the trouble. Marcinowski (22), how- 

 ever, does not agree with this, and after conducting an experiment 

 in which 90 per cent of the infected seedlings died while still young, 

 concluded that as a rule plants succumb before maturity when dis- 

 eased at an early stage of growth. At any rate, leaf and stem symp- 

 toms of the disease are less common, as well as less noticeable, on the 

 older plants. Maturing plants may be decidedly dwarfed, however, 

 somewhat yellow in color, and show a curling of the upper leaves, as 

 may be seen in Plate I, G. 



Leaf rolling, however, which is of more frequent occurrence than 

 the dwarfing and yellowing, is not always an indication of the nema- 

 tode disease, since it may be caused by other factors. While leaf 

 symptoms usually occur, they may be entirely absent, and yet, at the 

 maturity of the plant, the head may be found to be severely infected. 



Most positive and clear evidence of the disease can be detected by 

 a carefu] examination of the heads of the plant at maturity. Dis- 

 eased spikes (PI. Ill) are usually reduced in size, especially in 



