AERIAL GALLS OF THE MESQUITE 
F. D. Heald 
[With Figure 2 on Plate 117] 
During work upon a plant disease survey in the vicinity of 
San Antonio, Texas, 1 my attention was called to the frequent 
occurrence of galls upon the twigs and branches of the mesquite 
( Prosopis glandulosa Torr.). The following quotation is from 
the publication dealing with the survey mentioned : “ The large 
limbs and smaller branches of the mesquite sometimes show 
abnormal enlargements which are frequently globular or some- 
times elongated and sometimes greatly exceed the diameter of 
the branch on which they are produced. (Plate XV, figs. 2 and 
3.) Specimens have been obtained ranging from 1 to 8 or 10 
inches in diameter. The gall is produced by an abnormal growth 
of the wood, and cross sections of galls always show small brown 
specks where the wood cells are more or less disintegrated. 
These are distributed throughout the entire woody region. 
“ These galls are not of insect origin, and cultural work at- 
tempted has as yet failed to connect either bacteria or fungi with 
the disease, although both have been obtained.” 
The crown-gall organism, Bacterium tumefacicns Erw. Sm. & 
Townsend was strongly suspected of being the cause of the galls, 
but at the time of writing the bulletin referred to the authors had 
obtained no direct evidence of such causal relation. No oppor- 
tunity was afforded for detailed work on this subject, but Dr. 
Erwin F. Smith, of the Bureau of Plant Industry, very kindly 
furnished some cultures of B. tumefaciens which were used with 
the class in plant pathology in making some inoculations on the 
mesquite. 
The inoculations were all made on a large tree growing under 
natural conditions on the campus of the University of Texas. A 
1 Heald, F. D. and Wolf, F. A. A plant disease survey in the vicinity of 
San Antonio, Texas. Bull Bur. of PI. Ind. U. S. Dept. Agr. 226: 72. 1912. 
37 
