Annals 



of the 



Missouri Botanical Garden 



Vol. 10 SEPTEMBER, 1923 No. 3 



INDICATIONS RESPECTING THE NATURE OF THE 



INFECTIVE PARTICLES IN THE MOSAIC 



DISEASE OF TOBACCO 1 



B. M. DUGGAR 



ogist to the Missouri Botanical Garden, in Charge of Graduate Lc 

 Professor of Plant Physiology in the Henry Shaw School of Botany of 



Washington University 



AND JOANNE KARRER ARMSTRONG 



Research Assistant to the Missouri Botanical Garden 



Among plant pathologists there is to-day no topic of more 

 engaging interest and no problem more difficult than that of the 

 nature of the causal agency in mosaic and allied plant diseases. 

 Possibly we might extend this statement so as to comprehend at 

 the same time the causal factors involved in those types of vegeta- 

 tive variegation, or modified pigmentation, whether infectious 

 or not, which afford the decorative mottled, spotted, and striped 

 plants so much cultivated for foliage effects. 



At various times almost every conceivable view has been held 

 as to the nature of the etiological agent in tobacco mosaic, but 

 from the earliest experiments it has been perfectly clear that 

 the disease is transmissible. The great majority of workers have 

 accepted the evidence of the filterable character of the infective 

 agency, and it is this which gives to the disease much of its pecul- 

 iar interest. 



The relation of the true mosaic diseases to certain other types of 



1 This paper was read at the annual meeting of the American Philosophical Society, 

 Philadelphia, April 21, 1923. 



Ann. Mo. Bot. Gard., Vol. 10, 1923 (191) 



