ENTOMOLOGY. 269 



The worms which cause such diseased conditions of plants are very- 

 small and consequently are not readily detected excepting by those 

 possessing considerable experience with microscopic investigations. Fig. 

 2 represents the diseased root of the parsnip; the root of this plant was 

 selected simply because it required less space to illustrate it than the dis- 

 eased roots of apple or pear before you in the exhibition case, and also be- 

 cause it is a more typical specimen. You will perceive that the abnormal 

 growths upon the root of parsnips appear as irregular, knotty enlarge- 

 ments, from two to ten times the normal diameter of the roots. Such 

 knots are at first smooth, but become rough with age and crack in vari- 

 ous ways, until decay of the tissues sets in, and they gradually disappear. 

 As may be seen in the illustration in Fig. 2, the tap-root and the earlier 

 lateral roots were attacked early in the season, and are partially decayed and 

 falling to pieces. The plant in its struggle for existence sends out new 

 roots, which in turn are attacked and deformed, There is a great variety 

 in the forms of these knots or galls even upon the roots of the same 

 plant. Their external form depends greatly upon the number of worms 

 infesting them, upon their distribution in the tissues and upon the spe- 

 cific peculiarities of the root itself. Such abnormal growths upon the 

 roots are usually called "root-knots." In Scotland they are called "root- 

 ill," "thick-root," "tulip-root," and "legging." In Germany they are 

 known as "warzelgallen." 



In the earlier stages of the disease the root-galls have a considerable 

 resemblance to the "potato-scab," but closer inspection will show that 

 they are quite distinct; although sometimes appearing upon the very 

 same potato. It we compare the root-galls with the so-called "club-foot" 

 of the cabbage, we also find considerable external resemblance, but closer 

 study will show that the root-galls before you are produced by an animal 

 with a complete and high organization, while the "club-foot" is caused 

 by a plant of the very lowest organization, one of the slimy moulds. 



If we take a root-gall produced by the presence of nematode worms, and 

 cut directly across it, and take a very thin shaving from the cut end, and 

 put it upon a slip of glass under the microscope, the cause of the disease 

 will be revealed at once. In Fig. 3 such a thin section is illustrated, very 

 greatly magnified. The larger bodies represent two female cysts; the upper 

 one (a) is mature, the lower one (b) is in an earlier stage of development. If 

 the female cyst is very old the cavity is occupied by eggs in different 

 stages of development, and by thread-like bodies, the larvas. This is indi- 

 cated in Fig. 4. Eggs and larva? float in a gelatinous, granular substance, 

 the remains of the parent worm. If the knife in making such a thin sec- 

 tion should pass by the side of an animal without injuring it, the cavity 

 exposed will then contain a perfect animal, quite different in form accord- 

 ing to age or surroundings. 



To study a mature female cyst we select the galls upon the roots of a 

 plant with softer tissues, or roots which are already softened by the inci- 

 pient stages of decay. Carefully breaking one we can with a little patience 

 soon discover yellowish, irregular oval bodies, one-hundreth to one-fiftieth 

 of an inch in diameter. With the unaided eye we can detect the head pro- 

 jecting as a minute point on one side, as in Fig. 4. If we magnify this 

 minute body about 100 times we notice that a gravid female cyst is before 

 us. The handle-like part of this gourd-shaped body is the head ; the 



