MOSAIC DISEASE OF TOBACCO. 75 



soil during the winter. Weak solutions of formalin did not kill the virus, but 

 heating to boiling point did. Fresh, unfiltered juice was more effective than an 

 equal amount of filtered juice. He found that soil around diseased plants may 

 infect the roots of healthy plants, but he did not determine whether direct trans- 

 ference is possible through healthy root surfaces, or whether insects, by injuring 

 the roots, favored infection. He defines the milder form of the disease as a suffer- 

 ing of the chlorophyll bodies. Later a general disease of the plasmatic contents of 

 the cells sets in. 



In field conditions as a final stage the swollen green areas become marked with 

 small dead spots, but these did not appear on plants grown under glass. Under 

 certain conditions he observed that plants apparently recover from the disease; 

 i.e., the new growth appeared to recover. He found that the infective material, 

 whatever it might be, could be transported through considerable distances in the 

 plant, but could cause the disease only in the dividing cells. He assumed the 

 virus to be a non-corpuscular, fluid-like material, which had the power of growth 

 when in contact, in a sort of symbiotic way, with the growing cells, — "a living 

 fluid contagium." 



Shortly after Beijerinck's paper, Sturgis ^ published a critical review of the work 

 done on the disease up to that time, with numerous valuable results and observa- 

 tions made in Connecticut, where the trouble is known as "calico" or "mottled 

 top." 



The results obtained by Sturgis and observations made by him on 

 tobacco in Connecticut bore out the statements of other careful and 

 critical workers, and greatly cleared up the field for further investigation. 

 He came to the conclusion that on close, clayey soils the disease may be 

 more abundant than on an open, porous soil. The disease is not conta- 

 gious, but he could not state definitely as to its infectiousness; it is not 

 caused by fungi, nematodes or parasitic insects, and the facts observed 

 by him were not favorable to the theory of bacterial origin. He also 

 came to the conclusion that the disease is not inherent in the seed, and 

 looked upon it as a purely physiological trouble brought about by sudden 

 interruptions of the normal plant metabohsm. Koning, ^ in his work, 

 verified much of the work of Beijerinck and Mayer, and Woods' later 

 verified the work of these investigators and pointed out that in the 

 diseased leaves there was an excess or excessive activity on the part of 

 an enzyme belonging to the oxidases, and that the power of oxidation in 

 the cells was inversely proportional to the amount of chlorophyll present, 

 using the color as a basis of comparison. He also pointed out that there 

 was a marked structural difference between the cells of the dark green 

 and light green areas, and proved to his own satisfaction that the light 

 green areas are the truly diseased portions, a fact that will be referred to 

 later in this paper. In a later careful investigation of the disease Woods * 

 arrived at the following conclusions, which were a great stride forward in 

 our understanding of some phases of this baffling disease. He states : — • 



» sturgis, W. A.: Mosaic Disease of Tobacco. Conn. Agr. Exp. Sta. Rept., 250-254 (1898). 

 2 Koning, C. J.: Die Flecken oder Mosaikkrankheit des hollandischen Tabaks. Zeitschrift 

 fur Pflanzenkr., 9: 65-80. 



' Woods, A. F.: Inhibiting Action of Oxidase on Diastase. Science, n. s.. No. 262, 17-19. 

 « Woods, A. F., loc. cit. 



