262 BACTERIA IN RELATION TO PLANT DISEASES. 



immunity. Since all this is not evident to the eye, too small a number of plants should not 

 be isolated, and the seed from each must be watched, kept, and sown separately. 



Suppose the case that one plant of the 40 was by inheritance so much more resistant 

 than the others that under exactly similar circumstances and on the same kind of soil 

 mortality among its Offspring, instead of being from 60 to 70 per cent, was only 5 per cent, 

 while all the rest were barely alive as the result of infection. Now, what would happen if the 

 seed of the 40 plants were mixed ? The mixed seed would give a crop which under the same 

 conditions and on the same kind of soil and with the same amount of infection as the year 

 before, would again show 60 to 70 per cent dead plants. The one superior plant has no 

 noticeable influence on this mixture with the 39 others, and the result is that one must say : 

 "This is just as bad as last year. This method amounts to nothing. Away with it!" 

 If one had, on the contrary, kept this seed separate and planted its offspring separately, then 

 it would be evident that of the 40 selected mother-plants there were 39 worthless ones and 

 but one which would be of service for further testing. 



Thus in two respects the above-described method of work (that is, the method having, 

 as its special purpose, the obtaining of an immune or more resistant race of tobacco) differs 

 from the one customarily employed : 



(1) The seed-plants are not selected from the best soil, but preferably from the "sick soil" or 

 places where the loss from the slime-disease has been very great. The chance of resistant individuals 

 becoming conspicuous there is much greater than in places where not a single plant has been exposed 

 to the disease, and thus no plant gets the opportunity of showing its ability to withstand adverse 

 conditions. Twenty or thirty plants remaining sound in a field in which there is much disease give 

 more chance of results than a thousand from a field without any disease. 



(2) The seed from every one of the carefully selected plants is watched and sown separately. 

 Pedigree-culture is introduced. 



That these methods involve extra labor it is useless to deny, but without work one 

 accomplishes nothing. In great companies it will certainly be desirable to have a separate 

 "seed assistant," but by "seed assistant" must be understood something other than a 

 person who only sees to it that the company obtains the prescribed number of packages or 

 bottles of clean seed from well-cared-for, active plants. In my opinion he must be a man 

 who tries to select the types most suitable for certain kinds of soils. For this is one of the 

 great differences between the modern culture and the old: one chooses the plant-type 

 according to the kind of soil, well knowing that the soil may be improved but not changed in 

 character. Since it is now known that in Europe for clay, sand, and peat soils, or for com- 

 binations of all kinds of soils, definite varieties of grains, potatoes, cabbage, apples, etc., 

 are used, why should not the same principle be applied to Deli tobacco? Only when it is 

 certain that the Deli tobacco is a constant variety will efforts in this direction have no sense. 

 But the complete uniformity of the Deli tobacco is anything but decided. 



Every planter knows instances of his ability to recognize in the curing-room the tobacco 

 from a certain field by its color, texture (soepelheid), or by almost indescribable differences. 

 Sometimes variations in rainfall are the cause of the difference, but sometimes there are 

 variations occurring every year, caused by an entirely different composition of the soil. 

 In most cases the crop thus differentiated is less fine. Would it not be more profitable 

 to apply at once a system of strict selection with reference to the soil ? 



A principle that was very much applied in the past and still is followed is this: Use 

 for an upland plantation seed from a lowland plantation, and vice versa. The purpose of 

 this restoration (bloedverversching) has never been clear to me. Different companies have 

 also resumed growing their own seed, which is continually used for the same plantation; 

 a single company does this for every field. That is surely a step in the right direction. 

 But one must, in my opinion, go still further and give attention to the kind of soil rather 

 than to chance boundaries of the plots or experiments, so that one plantation must try 



