14 



the central cylinder is just beginning to form. Plate VI., fig. i shows 

 a section of a young and normal root at this stage. The cortical 

 tissue forms the larger part of the structure while the central cylinder 

 consists of a limited area of small cells in which a few ducts are 

 just beginning to develop. When a nematode attacks this young 

 rootlet it very soon begins to appear like those shown on the seedlings 

 in plate VII. Plate VI., figs. 3 and 4, show sections of these young 

 galls. In fig. 3 are seen three young worms which are just entering 

 the root (as shown from the exterior in plate VII., fig. i). There were 

 others no doubt on the opposite side which did not come into view 

 in this section. Comparing this with the normal rootlet in fig. i, we 

 notice first of all the increased size, clue principally to the increase 

 in number and size of the cortex cells. The central cylinder no 

 longer forms a definite mass in the center, but has separated into 

 several portions and occupies an irregular area. The few ducts 

 which have been formed are already distorted in direction and run 

 obliquely. Fig. 4 shows a similarly affected root at a somewhat 

 later stage. We see here a worm farther developed than those in 

 fig. 3, the broad, large celled cortex, and the central cylinder divided 

 into two parts in each of which appear several ducts and vessels 

 growing in an oblique direction. From this stage the abnormal 

 growth continues and the tissues become more and more confused 

 and distorted until the gall reaches a considerable size and has the 

 complicated structure shown in fig. 5. 



The effect upon the vital function of the plant produced by this 

 malformation of the root can be readily imagined. It is brought 

 about principally in two ways ; first, by the general interruption of 

 all the functions, and second and particularly by the interruption of 

 the normal flow of sap from the roots, caused by the distortion of 

 the ducts. Continuing the comparison of the root with the bundle 

 of tubes, imagine the latter to have become twisted, "kinked," 

 doubled up, and tied into knots. It is very plain then that the 

 passage of water through them would l)e hindered. The parts of 

 the plant above ground, absolutely dependent upon the roots for 

 moisture and food, must necessarily suffer from such an abnormal 

 growth in a measure proportionate to its extent. A few galls on the 

 roots produce no apparent effect. Where they are quite abundant 

 the plant becomes stunted and sickly, and where the roots become 

 completely covered with galls, as they do in badly infested soil, the 



