Annals 
of the 
Missouri Botanical Garden 
Vol. 8 NOVEMBER, 1921 No. 4 
THE SIZES OF THE INFECTIVE PARTICLES IN 
THE MOSAIC DISEASE OF TOBACCO 
B. M. DUGGAR 
Physiologist to the Missouri Botanical Garden, in Charge of Graduate Laboratory 
Professor of Plant Physiology in the Henry Shaw School of Botany of 
Washington University 
AND JOANNE L. KARRER 
Research Assistant to the Missourt Botanical Garden 
INTRODUCTION 
The present investigation is one of a series of studies in pro- 
gress or proposed with the idea of gaining further information 
concerning the constitution and behavior of the causal agency in 
the mosaic disease of tobacco or other mosaic diseases. We have 
undertaken this work with the feeling that all facts tending to 
throw new light upon any physical or chemical characteristic 
of the agency concerned might be helpful in the study of some 
or all mosaic diseases, and likewise, perhaps, in the study of 
ultramicroscopic agencies causally related to certain human 
and other animal diseases. The term agency rather than organism 
is employed because it is hoped to avoid any possible prejudice 
to the direction in which such research may lead. It is distinctly 
felt that any assumption tacitly ascribing such diseases, because 
infectious, to organisms of the known or usual types may serve 
in the end to restrict rather than broaden the investigation. 
The term ‘‘virus” will be used in this paper interchangeably 
with agency. 
It is, we believe, more frequently stated that the active agency 
ANN. Mo. Bor. Gard., Vor. 8, 1921 
(343) 
