FIELD STUDIES OF THE CEOWN-GALL OF SUGAK BEETS. 3 



Usually the galls with slender attachments occur singly, although there 

 may be several on the same beet, while the galls occurring in groups 

 usually have broad bases without any distinct line between the gall 

 and the beet. In the early stages of development — that is, when the 

 galls are young — their surfaces are bright, resembling the surf ace of 

 the beet proper and indicating active growth; but as the galls grow 

 older they become darker, especially if they are above the surface of 

 the ground. In this way their relative ages may be easily determined. 

 When galls have begun to form they usually increase in size most 

 rapidly on those beets that are making the most rapid growth. 



CAUSE OF BEET GALLS. 



The primary cause of the formation of crown galls on the sugar 

 beet and many other plants was for a long time in doubt. Few plant 

 diseases have given rise to more extended investigations than has 

 the so-called crown-gall. Different investigators have assigned the 

 origin of these abnormal growths to a great variety of causes, ranging 

 from slime molds to mechanical injuries. However, the investiga- 

 tions set forth in Bulletins Nos. 213 and 255 of the Bureau of Plant 

 Industry 1 prove conclusively that a bacterium or several closely 

 related bacteria are responsible for the origin and development of 

 these outgrowths belonging to the class of so-called crown galls. 

 The organism producing " tumors" is known as Bacterium tume- 

 faciens (Smith and Townsend) and the one producing "tuberculosis" 

 is designated as B. beticolum (Smith). 2 



The most extensive work on mechanical injuries as the cause of 

 gall formations on sugar beets has been carried on by Spisar. 3 There 

 seems to be no proof, however, that the organism which is capable 

 of producing galls on sugar beets was not present in the fields in which 

 Spisar carried on his experiments. It is apparent that a mechanical 

 injury offers a favorable place for the organism to enter the plant, 

 yet the indications are that gall formations will not result from 

 mechanical injuries unless the gall-producing organism is present. 

 In the field studies on the crown-gall of beets carried on by the writer 

 for several years, it has been frequently noted that when galls begin 

 to appear on the beets in a given field they are at first few in number, 

 increasing from year to year if beets continue to be grown in that 

 field. It has also been noticed that if badly infested fields are 

 followed one or two years with a grain crop and then returned to 



1 Smith, Erwin F., Brown, Nellie A., and Townsend, C. O., op. cit. 



Smith, Erwin F., Brown, Nellie A., and McCulloch, Lucia. The structure and development of crown- 

 gall: A plant cancer. TJ. S. Dept. Agr., Bur. Plant Indus. Bui. 255, 60 p., 2 fig., 109 pi. 1912. 



2 These organisms are described in Bureau of Plant Industry Bulletin 213, which may be obtained from 

 the Superintendent of Documents, Government Printing Office, for 40 cents, 10 cents additional being 

 required for postage to foreign countries. 



3 Spisar, Karl, tiber die Bildung des Zuckerriiben-Kropfes. In Ztschr. Zuckerindus. Bohmen, Jahrg. 

 36, Heft 1, p. 1-17, fig. 1-6; Heft 2, p. 57-72, fig. 7-11. 1911. 



