689 



less free organic acids are found\ Accordingly, the parts suffering wfth 

 the mosaic disease lack the ability to form sufficient reserve substances ; 

 and thus the mosaic disease, which, according to Hunger-, may also be 

 transmitted without the existence of any injury, simply by contact with the 

 hand, or, in grafting, be transmitted to the stock, belongs under albinism. 



While we still have no reason for restricting the last named phenom- 

 enon, because the white variegated plants, in spite of their greater sensitive- 

 ness, form desirable specimens for our gardens, yet, the need of earnest 

 regulations for combatting the mosaic disease, is most imperative and these 

 have often been tried. According to Koning liming the soil has proved to 

 be the best method. Hunger also proved good results by fertilizing with 

 bone meal and gives warning primarily against an excessive chemical ferti- 

 lization. In my opinion the disease is a result of inbreeding, which can be 

 overcome successfully by decreasing the supply of nitrogen and by increas- 

 ing the lime. 



Wood says", "Overfeeding with nitrogen favors the development of 

 the disease and there is some evidence that excess of nitrates in the cells 

 may cause the excessive development of the ferments causing the disease." 



The choice of seed also deserves especial attention as is evident from 

 the statements of Bouygeres and Perreau*. These investigators took seed 

 from plants, in the midst of a diseased field, which up to the time of har- 

 vesting had remained free from the mosaic disease. They obtained 98 per 

 cent, of healthy plants. These were, at any rate, capable of being infected 

 in wounds brought in contact with parts having the disease. Special con- 

 sideration should be given primarily to the soil. In earth, on which tobacco 

 had been grown for some time, healthy seed very easily became diseased^. 



Pox OF Tobacco. 



We have mentioned already, in discussing the mosaic disease, that other 

 phenomena of discoloration have often given rise to much confusion. An 

 example of the latter is furnished by the pox disease. Iwanowski and 

 Poloftzoff*' have called attention to the difference between this and the 

 mosaic disease. For three years they studied this disease in Bessarabia, 

 having been commissioned by the Russian Department of Agriculture. 

 According to Hunger", the disease manifests itself in the appearance of 



1 Hunger, De Mozaik-Ziekte bij Deli-Tabak. Deel I. Mededeelingen uit S'Lands 

 Plantentuin LXIII, Batavia 1902. 



2 Hunger, On the spreading' of the Mosaik-disease (Calico) on a tobacco field. 

 Extr. Bull. d. I'Institut Bot. de Buitenzorg 1903, No. XVII. 



3 Observations on the mosaic disease of tobacco, Washington 1902, p. 24. 



4 Bouygeres et Perreau, Contributions a I'etude de la nielle des feuilles du 

 tobac. Compt. rend. 1904, CXXXIX, p. 309. 



5 Behrens, J., Weitere Beitrage zur Kenntnis der Tabakspflanze. Landwirtsch. 

 Versuchsstat. 1899, p. 214 ff and 482 ff. 



6 Iwanowski und Poloftzoff, Die Pockenkrankheit der Tabakspflanzen. Mem 

 de I'Acad. Imp. de St. Petersbourg 1890, s6r. VII v. XXXVII,, 



7 Hunger, Zeitschr. f. Pflanzenkrankh. 1905, p. 297. Here also pertinent 

 bibliography. 



