BULLETI]^ l^o. 175. 



DEPARTMENT OF BOTANY. 



MOSAIC DISEASE OF TOBACCO.^ 



BY G. H. CHAPMAN. 



Introduction. 



The observations and conclusions reported in the following pages are 

 the results of several years of more or less continuous investigation on 

 the part of the writer, and deal with the probable causes, occurrence, 

 appearance and methods of control of this well-known disease of tobacco 

 and related plants. Enough has been accomplished so that it is believed 

 wise to add still another paper to the already long list of literature which 

 has been pubUshed on this disease. During the time in which these 

 experiments have been in progress much new literature has appeared 

 dealing with this subject, some of which has helped the writer by verifying 

 his results and by bringing out new facts concerning the disease; but, on 

 the other hand, some of the work appears to have been done in a hasty 

 manner, and possibly erroneous conclusions drawn in some cases, thus 

 adding to the large amount of confusing subject-matter which has to do 

 with this disease. The experiments carried on by the writer were begun 

 in a general way in 1907, and have been repeated several times during the 

 years subsequent to that date, new lines of investigation both in the 

 field and laboratory having been added as occasion demanded. Some 

 considerable time has been spent in verifjdng the results obtained by other 

 recent investigators, and an attempt has been made to gather together in 

 a broad, general way, as well as in detail, aU the reliable information 

 possible about this interesting disease, as well as to bring out new facts in 

 regard to it. More attention has been given to the biochemical aspects 

 of the problem than has heretofore been done by investigators. 



> Also presented in part to the faculty of the graduate school of the Massachusetts Agricultural 

 College, June, 1916, as a major thesis in partial fulfillment of the requirements for the degree of 

 doctor of philosophy. 



