40 



Letters on the Diseases of Plants. 



interested in the sugar-beet industry, but to little purpose. Year by year 

 the pest grew worse, — more and more land had annually to be abandoned by 

 the beet-grower. At this point the philosophical faculty of the University 

 at Leipzig oifered a prize for the best investigation of the cause oE the 



Eiibenmiidigkeit. The prize was awarded 

 to Strubell for an investigation whose 

 results are detailed on page 170, Vol. I of 

 the Agricultural Gazette of N.tS.W., under 

 the head of T. schachtii. 



Professor Kiihn, making Strubell's in- 

 vestigations the basis of his reasoning, 

 now devised a plan for trapping the 

 larvee. Noting that, according to Stru- 

 bell's investigations, the larv?e on enter- 

 ing the young beet plant became mature 

 in about five or six weeks, he pre- 

 dicted that if the plants were pulled 

 at the end of four weeks, the worms 

 in them would die without producing a 

 new brood. It will be seen that Pro- 

 fessor Kiihn's plan was based on a 

 careful perusal of the life-history of the 

 Tylenchus. If the plant should be al- 

 lowed to remain five weeks before 

 being pulled, the worms would, it is 

 true, be killed, but not so the eggs ivhich 

 in Jive weeks the females loould have 

 produced. These eggs would ultimately 

 hatch and the pest continue. But after 

 precisely four weeks, even the oldest 

 worms in the roots would not yet have 

 produced eggs, and, being at that time 

 motionless sacs, incapable of boring their 

 way out, must perish from starvation if 

 the host-plant should suddenly die. In 

 other words, Kiihn proposed to make traps 

 of the young plants, and naturally chose such plants as are loved best by 

 the worms. Sugar-beet was selected as the plant likely to entrap the 

 greatest numbers. 



The result of the experiments based upon Kiihn's plans was a brilliant one. 

 A piece of ground, so badly infested as to be useless to the sugar-beet grower, 

 was sown with sugar-beet. After four weeks the plants were pulled, and 

 another lot of seed sown. The experiment was repeated a third time, if 

 necessary, and it was then found that the pest was controlled. The time 

 occupied was about three months. The plants whose roots were used as 

 traps could be turned to account as fodder or fertiliser, so that the twelve 

 weeks were not a dead loss. In Kiihn's first experiments the plants were 

 pulled by hand. That operation was expensive, and led to a trial of ploughing 

 up the trap-roots, and this plan was found to answer almost equally as well. 

 It is beforehand to be supposed that the Australian gall-worm may be 

 trapped in the same way as T. schachtii, but the time required for its develop- 

 ment is not yet accurately known. I have no data for giving the precise 

 length of time required for the lai'vse to mature in roots. The most I can 

 say is that it is probably less than that required by the sugar-beet gall-worm. 



Fig. 62. — Male gall-worm, i, mature 

 male, x 65 ; li, head of same, x 450 ; 

 III, larval male, inside of its cast off 

 skiu, X 50; IV aud v, cross and longi- 

 tudinal sections, x 350 ; vi, lateral 

 and ventral view of tail, s 225; s, 

 spear; b, bulbs; i, intestine; s 2, 

 spermatozoa ; c, cuticula ; v, vas 

 deferens ; d, end of ejaculatory duct ; 

 ■ps, penes or spicula; a, anus. 



