THE MOSAIC DISEASE OF TOBACCO. 23 



Mayer has shown that the mosaic virus is killed near a temperature 

 of 176° F. Iwanowski x first demonstrated that the sap of mosaic 

 plants was still infectious after passing through a Chamberland 

 filter. Beijerinck 2 and Koning 3 later obtained the same results. 

 Beijerinck 4 states that he found the unfiltered juice, volume for 

 volume, more effective than the filtered. The writer has filtered the 

 virus through a Berkfeld filter, but the perfectly clear filtrate remains 

 as highly infectious as the unfiltered sap. Just how long this filtered 

 sap will retain its virulence has not been determined. Tests by the 

 writer show that it was still infectious after being bottled for four 

 months. Beijerinck, also, found the filtered sap infectious after being- 

 kept more than three months and mentions that weak solutions of 

 formalin did not kill the virus, while heating to the boiling point 

 did. Beijerinck found that dried mosaic leaves retained their infec- 

 tious qualities for two years. The writer has found that air-dried 

 mosaic material, ground and bottled, was still highly infectious at 

 the end of 18 months. In fact, inoculation with dried material mixed 

 and macerated with water appears to be the surest method of com- 

 municating the disease to healthy plants. 



Experiments with fresh mosaic leaves placed in soil in large pots 

 kept out of doors during the winter of 1911-12 seem to indicate that 

 the virus in this condition retained its infectious properties to some 

 extent. It was thought that these leaves would decay, but the con- 

 tinuous, severe freezing weather evidently kept this process in check. 

 Portions of these buried leaves, practically dry and green in color, 

 were ground into a paste with water and pricked into young, healthy 

 plants. The results of inoculations were far less certain than with 

 fresh juice or bottled mosaic material. Healthy leaves left out of 

 doors under the same conditions did not produce the disease at any 

 time. 



Numerous experiments have also shown that the mosaic virus pre- 

 served in ether, toluene, or glycerin retains its infectious properties 

 for a considerable length of time. The mosaic virus preserved as 

 follows was still infectious to healthy plants on March 5 : 

 10 c. c. virus+l c. c toluene prepared. December 9. 



1 Iwanowski, D. Ueber zwei Krankhoiten der Tabakspflanze. Land- und Forst- 

 wirtschaft, 1892. (Ilussisch.) Abstract in Beihefte, Botanisches Centralblatt, Jahrg. 3, 

 p. 266-268, 1893. (Original not seen.) 



2 Beijerinck, M. W. Ueber ein Contaginm vivum fluidum als Ursache der Fleekenkrank- 

 heit der Tabaksbliitter. Verhandelingen, Koninklijke Akademie van Wetenscbappen, Am- 

 sterdam, sect. 2, deel 6, no. 5, 22 p. 2 pi., 1898. Abstract in Centralblatt fur Bakteri- 

 ologie [etc.], Abt. 2, Bd. 5, No. 1, p. 27-33, 1899. 



3 Koning, C. J. Die Flecken- oder Mosaikkrankheit des holladischen Tabaks. Zeitscbrift 

 fur Pflanzenkrankheiten, Bd. 9, Heft 2, p. 65-80, fig. 1-2, pi. 2, 1899. 



4 Beijerinck, M. W. De l'existence d'un principe contagieux vivant fluide, agent de la 

 nielle des feuilles de tabac. Archives Neerlandaises des Sciences Exactes et Naturelles, 

 s. 2, t. 3, livr. 2, p. 164-186, pi. 5-6, 1899. 



