13 



If now a section be made of a fair sized nematode gal], a consider- 

 able difference in the arrangement of the tissues will be seen. The 

 central cylinderno longer has its regular outline and central position, 

 but forms an irregular, misshapen area, extending nearly to the out- 

 side of the root in some places, while in others it is far from the 

 surface. The cortex also has an irregular shape and thickness, but 

 it is much thicker than in the normal root. Here and there on the 

 surface of the section will usually be seen the female worms or their 

 remains, some near the edge and others at various depths in the root. 

 Examination with the microscope shows a great disarrangement of 

 all the root tissues. (PI. VI., fig. 5). The cells of the cortex are 

 increased in number and size, being affected especially in the vicinity 

 of the worms, which are located mostly at the inner edge of the cortex 

 at its junction with the central cylinder. In the latter portion of the 

 root serious changes have taken place, as a result of which the injury 

 to the plant is mostly to be ascribed. The ducts and smaller vessels, 

 instead of running directly through the root as in the normal speci- 

 men are greatly distorted and deviated so that many of them run 

 directly at right angles to their natural course, i. e. across the root, 

 and a cross section shows their sides, which are marked with lines and 

 dots on their wall, instead of their open ends as in the section of the 

 normal root. Where one of the worms is located near or in the 

 cylinder the vessels grow in such a way as to form an irregular mass 

 completely enclosing it, and even where the nematode is in the midst 

 of the cortex they are greatly deviated from their natural course. 

 The size and shape of the galls, as we have already pointed out, 

 depends largely upon the number and location of the worms, and 

 also upon the kind of plant, but not, as far as we know, upon the 

 worm itself. That is to say, we cannot conclude that galls of a 

 certain shape indicate a particular kind of worm, for while each of 

 the affected plants has a gall more or less peculiar to itself, the 

 worm is the same in all. Large galls are formed where several 

 worms attack the root at the same place. If they be close together 

 and distributed on all sides of the root the resulting gall will be of 

 quite regular shape. Irregular galls are formed where several worms 

 locate on one side of the root, or at short distances from one another 

 so that several small galls grow into one. Most of the galls start 

 when the roots are very young, or on the younger portion, near the 

 tips of older roots. Here the tissues are in a formative stage and 



