THE BEOWN EOOT ROT OF TOBACCO AND OTHER PLANTS O 



larity to brown root rot as it occurs on tomatoes in the writers* ex- 

 periments. Byars and Gilbert (2) also report a Rhizoctonia disease 

 on tomato which resembles brown root rot of tobacco. These authors 

 apparently based the Rhizoctonia relation, however, on microscopic 

 examination only. 



If examined from an agronomic point of view, it may be found that 

 we are dealing with an old problem under a new name. One of 

 the earliest scientific explanations of reduced soil fertility was based 

 on the development of toxins in the soil, resulting either directly 

 from excretions of the living roots or from the products of decom- 

 position of the preceding crops. 



This subject has been the ground for considerable controversy, 

 and whether or not toxins actually exist in field soils can not 

 be regarded as an established fact. Nevertheless, the results of 

 several investigators, from those of Macaire (i^), as early as 1832. 



Fig. 4. — A field of tobacco following timothy sod near Cambridge. Wis. The single 

 row of large plants follows a backfurrow. the treatment otherwise being the 

 same as in other rows 



to the recent work oi Garner, Lunn, and Brown (5), establish be- 

 yond any reasonable doubt that crops often affect the yield of suc- 

 ceeding crops deleteriously to a marked degree. 



This subject has so recently been reviewed by Garner and his 

 associates (5) that the reader is referred to the publication cited, 

 which is, moreover, closely related to the present bulletin, since 

 its senior author was able to observe the experimental plats at Upper 

 Marlboro, Mel., during several seasons and to experiment with soil 

 samples from those plats. Studies on these soils seem to justify 

 the belief that in the broadest sense the problem in Maryland is 

 essentially similar to that described in this bulletin. The symptoms 

 of brown root rot were not nearly so evident in Maryland as in 

 the Connecticut Valley, but it is believed that the condition re- 

 ferred to as brown root rot played some part at least in the experi- 

 mental results obtained at Upper Marlboro. 



