74 MASS. EXPERIMENT STATION BULLETIN 175. 



Historical Summary. 



In the following paragraphs is given a brief r^sum^ of the more important 

 work done on the mosaic disease of tobacco up to the present time, and 

 as an excellent critical review of the Hterature, etc., up to 1902 is given by 

 A. F. Woods 1 in his work on the subject, the same is quoted in full below. 

 He states : — 



Adolph Mayer ^ was the first to make a careful study of the trouble. He demon- 

 strated that it could not be caused by an insufficient supply of mineral nutrients. 

 He found as much nitrogen, potassium salts, phosphates, calcium and magnesium 

 present in the soils and plants v/here the disease occurred as in the soils where the 

 disease did not occur. He also found that the trouble was apparently distributed 

 over the field without regard to the soil conditions. 



Since tobacco requires much lime, liming the soil was tried, but the disease was 

 not prevented thereby. Mayer further kept hotbeds in some cases rather moist, 

 in others dry, and then again, richly or poorly manured with nitrogen; but in no 

 case could he determine that the conditions in question caused the disease. He 

 also found that variations in the temperature of the hotbeds apparently had no 

 effect; neither did crowding, which produced partial etiolation, appear to have 

 any effect on the disease. Seeds from flowers in which self-fertilization was pre- 

 vented he found to be just as susceptible to the disease as seeds produced without 

 such precautions, but on the soil on which the disease had once appeared it was 

 again produced. According to his observation, also, the trouble was not often 

 found on soil used for the first time for tobacco. He further proved that the 

 juice of the diseased leaves injected with the juice of healthy plants did not develop 

 the disease. He was not able to produce it by injecting diseased juice into other 

 solanaceous plants. Where the diseased juice was injected into tobacco the same 

 trouble developed in from ten to eleven days. Heating to 60° C. did not destroy 

 the infectious substance; at 65° to 75° it was attenuated, and at 80° it was killed. 



After Mayer had shown the absence of animal and fungous parasites he. sup- 

 posed bacteria to be the cause of the disease, but all his efforts with bacteria cul- 

 tivated from the surface of diseased leaves, and also with different mixtures of 

 bacteria, failed to produce it. Nevertheless, he thought that there must be certain 

 pathogenic bacteria present in those soils in which the disease appeared, and 

 therefore proposed to change the soil in the hotbeds and to devote the fields where 

 tobacco had been cultivated to other crops. He also recommended the use of 

 mineral rather than organic manures. 



These general results were confirmed by several subsequent investigators. Not, 

 however, till Beijerinck ' took hold of the question was much of importance added 

 to our knowledge of the malady. He proved the absence of bacteria in the devel- 

 opment of the disease. He showed that the juice of the plant filtered through 

 Chamberland filters, while remaining perfectly clear and free from bacteria, still 

 retained the power of infection. A small drop of it injected hypodermically into 

 the growing bud was sufficient to give the plant the disease. He found that only 

 dividing (meristematic) cells can become diseased. Diseased tissue kept its in- 

 fectious qualities even after drying, and retained its injurious properties in the 



> Woods, A. F.: Observations on the Mosaic Disease of Tobacco. U. S. D. A., Bur. Plant Ind. , 

 Bui. No. 18 (1902). 



2 Mayer, Adolph: U'ber die Moaaikkrankheit des Tabaks. Landw. Versuchsstation, 32: 

 4 51^67 (1886). Review of the same article in Journ. of Mycology, 7: 382-385 (1894). 



' Beijerinck, M. W.: Verhandelingen der Koninklijke Akademie van Wetenachappen te 

 Amsterdam. Deel 6: No. 5. See also Centb. f. Bakt., Par., etc., II: 5: 27-33 (1899). 



