WILT-DISEASES OF TOBACCO. 261 



many can not be estimated. Apparently there are only a few, and in any event they are not 

 of such a kind that one can go out into the field and select them. The Deli seed is much 

 purer in Sumatra than that, for example, which was grown some years ago in America, when 

 Shamel found 1 1 types in one field. The "Deli seed " with which this field in Connecticut 

 was planted came from Florida and may thus have been mixed with other sorts. 



Proofs that in the Deli tobacco hereditary differences still appear are but two, namely, 

 the giant plants and the .Strain B 1-5, which in 1906 was obtained in a mosaic-disease test, 

 undertaken with Helvetia and a couple of other varieties. These plants, B 1-5, blossomed 

 in 1907 about 10 days earlier than the others, formed thus a premature type, and this year 

 the sixth generation again blossomed 10 to 12 days earlier than the others. Dr. Diem found 

 in 1907 that the average difference in height between B 1-5 and the race B 1-1 was almost 

 half a meter to the disadvantage of B 1-5, which also produced on an average four leaves 

 less. Moreover, these differences, which indeed that one year were somewhat greater than 

 in other years, have persisted, so that B 1-5 is to be considered a separate type. 



Besides these two examples there are perhaps more. One often finds in the plantations 

 plants which vary. When it is a single example which is distinguished by broad or small 

 leaves, there is no reason to consider it immediately a separate type. On the contrary, 

 when one gets this impression from a whole plot (afdeeling) it proves that two forms, 

 a broad-leaved and a small-leaved type, have been planted side by side. I remember such 

 a case in an upland plantation in 191 1, and I am not the only one who was subject to this 

 impression. 



Up to the present there have been but few experiments in which selection has been 

 exercised in the sense of pedigree-culture, such as was advised as early as 1907. One gener- 

 ally restricts himself to the maintenance of a fine stock from which the less vigorous plants 

 are removed; thus a form of "mass-selection." Unquestionably this is one means of keep- 

 ing the culture up to the mark, but the chance of making any advance in this way is ex- 

 tremely slight. To be sure by this method the seed of the best plants is always collected 

 and when there happens to be among them a couple of extra good plants which will produce 

 better offspring, the seeds of these are also gathered, and are not lost. But this seed of the 

 uncommonly good plants becomes diluted with the quantity of common seed which out- 

 number them by some hundreds or thousands. On sowing, the descendants of the best 

 plants are lost in the great mass. In case the circumstance should arise that the descend- 

 ants of such a plant with large leaves should grow somewhat less rapidly in their youth, 

 something more happens, namely, these will disappear during the thinning out, with the 

 result that in the crop, the same as the previous year, but few examples of the better type 

 will appear. If now, again, on a good piece of ground a portion of these be selected for seed 

 plants, then is one just as far advanced as the year before a single plant of the better type 

 here and there in the great mass. Had one, however, kept separate the seed of a couple of 

 extra fine plants, then it would soon be evident whether the wished-for characteristics were 

 hereditary or not. 



A concrete example will make this still clearer. On two plantations there has been 

 made this year, at my request, a beginning in selection-tests for immunity to the slime- 

 disease. In one plot on one of these plantations, where there had been much damage from 

 the slime-disease, there were in the worst field 40 plants which had remained intact (zich 

 goed gehouden hadden), and which were guarded from cross-pollination by gauze sacks. 

 The plants had the greatest chance of becoming infected, since the mortality on this spot 

 had amounted to at least from 60 to 80 per cent, and the rest, especially toward the last, 

 appeared to be very much diseased. At the present time it (the disease) is not evident on 

 the plants, which appear to the eye to be sound. It is possible that by chance they have 

 not come into contact with virulent bacteria and possibly in case of an infection they might 

 be very susceptible, but there is also the chance that some of them would be somewhat 

 more resistant, and a single one much more resistant than the average, to say nothing of 



