The observations and conclusions reported In the following pages are the results of several years of noro or less continuous investigation on the part of the writer, and deal with the causes, occurrence, appearance and the probable methods of control of this well known disease of the tobacco and related plants iSnough has oeen accomplished so that it is believed wise to add still another paper to the already long list of literature which has been published on this disease. During the time in vhich 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 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 are drawn in some cases, thus adding to the already large amount of confusing subject matter which has to do with this disease.