178 Agricultural Gazette. 



essential sets of organs, the rootlets, become aborted. The absolutely 

 essential food due the plant from the soil is cut off, and unable to live 

 upon air alone it dies. 



Let us now turn to the disease as manifested in the potato. Pig. 8 repre- 

 sents more or less spherical growths which appear in the 

 substance of attacked potatoes. These growths seem always 

 to bo connected with distorted vascular tissue. Tliey are 

 found to vary much in size, and there seems little doubt 

 that the " knobs," characteristic of the disease as it appears 

 on the potato, are the result of these small beginnings. 

 Each such body is composed of a thick outer wall, and an 

 inner granular mass. 



These appearances in the parsnip and potato lead me to 



suspect that the abnormal growths caused by Ti/lcnchtis 



... «/T««r«a« are probably to be compared to the galls produced 



(I, coll containing ' . .- - i ,, , o, J. . ,, 



starch grains ; b, on leaves by various insects. It is well known that ieatgalls 



secn"fn' attacked ^^'^ causod in the first place by a disturbance of the vascular 



potato; c, vesica- tissues. The gall-producing iusect commonly pierces a veiii 



lar tissues x 40. ^^ ^ j^^ j^^^l ^^,jj.j^ • ^^ o^jpoj^jto ^ ^,,1,^,1 depositing its egg. It 



is a common belief that the gall appears in consequence of a fluid injected 

 by the insect at the time of laying the egg. I do not know whether this 

 belief is supported by any good evidence. Possibly the mere irritation of 

 such a foreign body as the egg of an insect or the wriggling larva hatched 

 from it may be sufficient to account for the gro>vth of the gall. Certainly 

 there are difficulties in explaining the growth caused by Tylcnclins on the 

 theory of the irritation being caused by an excretion. The more natural 

 explanation seems to be that the abnormal growths are the result of mechanical 

 irritation. 



If I am right in comparing the swellings produced by Tylenchus arenarius 

 to the leaf-galls produced by insects, then the former should be called root- 

 galls, and the Tylenchus itself may appropriately bear the name of the gall- 

 worm. Dr. Neal has called the disease, as it appears in the United States, 

 the root-knot disease. His name can have no reference to knots, the places 

 where branches originate, otherwise it would be entirely inappropriate, but 

 refers to the characteristic appearance produced by the disease on rootlets, 

 which has been compared to the appearance of a thread with knots tied in 

 it. The German name for the disease caused by Tylencliiis Scliaclitii is 

 Riibenmiidigkcit— that is, turnip-lassitute or beetroot-lassituto, referring to 

 the tardy growth of the diseased plants. I believe both these names will be 

 supplanted by the simple term "root-gall" (Wurzelgalle), which may be 

 thus defined— abnormal growths on roots and rootlets, caused by the attacks 

 of gall-worms. 



Historical. 



It is not until within recent years that ^\e have arrived at an accurate 

 knowledge of the habits of the gall-worm, although the disease root-gall has 

 been known for a very long time. How long root-gall has been recognized 

 as a distinct disease of the sugar-beet of Europe 1 am unable to say, but 

 that it is very many years is certain. The root-gall of the peach has, 

 according to Dr. Neal's exceedingly useful pamphlet, been known to the 

 white people of the South Atlantic and Gulf States of America since the 

 earliest settlement of the country ; and, according to the same authority, 

 reliable agriculturists state that the disease is indigenous there, they having 

 seen it in places where neither trees nor jjlants had ever been introduced 



