4 CIECULAR 3 76, U. S. DEPARTMENT OF AGRICULTURE 



Fig. 3. — Typical trees classified as possessing large galls, one (left) showing the 

 wooll.y-knot type and the other a simple form of ciown gall 



In the experiments of 

 1925 the organic-mercury 

 treatment was given to 2,619 

 grafts, representing a num- 

 ber of different varieties, 

 with the result that the 

 total number of trees ob- 

 tained at digging time with 

 both large and small galls 

 amounted to 6.1 per cent, 

 as compared with 32.6 per 

 cent on 2,619 untreated 

 grafts of the same varieties 

 Avhich were used as checks. 

 The proportion of the total 

 number of large galls in the 

 treated grafts of all varie- 

 ties w^as 2 per cent and in 

 the untreated or check 

 grafts 28.7 per cent, as 

 shown in Table 1. 



Figure 5 represents a typi- 

 cal lot of trees resulting 

 from the use of the organic- 

 mercury compound. This 

 lot was selected because it 

 illustrates about the average 

 control obtained in the ex- 

 periments in 1925, whereas 



* 

 t 



Fig. 4. — One of the types of trees classified 

 doubtful 



