— 11 - 



The experiments that hâve been made up till now by 

 several investigators to prove the easy transference of 

 calico, were always conducted — either bij injection ofdi- 

 seased juice, or by inoculation of diseased plantmaterial — , 

 while it was further plainly proved, that the soil in 

 which a diseased plant lias been growing is also able to 

 produce the disease. (Le. page 57 — 59). 



Koning ventured the supposition from his own expérience, 

 that when a calicoleaf is rubbed between the Angers and 

 the moist flnger is afterwards laid on the surface of a wound, 

 caused by pluching off the leaf from a healthy plant, 

 the spots always appeared on the youngest leaves of the 

 plant tnree or four weeks later: „Es scheit mir nicht 

 „unmôglich, dass die Personen, welche mit dem Kôpfen 

 „der Ptlanzen und dem Ernten der Blâtter beauftragt 

 „sind, mit ihren von kranken Blattteilen infizierten 

 „Fingern den Ansteckungsstoff auf gesunde Pflanzen brin- 

 ^gen kônnen ; daher im Spatsommer die zahlreichen Fâlle, 

 „wo die Geizen und jungen Blâtter die Fleckkrankheit 

 „zeigen." l ) 



This hypothesis is once more based on the transferring 

 of diseased juice — either from the stem (at topping), 

 or from the leafstalk (at harvesting); which is only a 

 modified method of the already long known grafting. 

 Notwithstanding this however if the above mentioned 

 method of infection could be proved, the gênerai opinion, 

 that the coolie is not without fault in the spreading of 

 this disease on the fleld would hâve some foundation. 



During my stay in Deli this year, experiments were 

 arrangea so as to investigate if really any connection 

 could be discovered between the treating of the tobacco- 

 plant and the appearing of calico afterwards. 



The experiment was extented even beyond Koning' s 



!) C. J. Koning. Der Tabak, pag. 33. 



