Destruction of Charlock, 



357 



strength would not injure the corn, and on the other hand 

 that weaker solutions would not effect the desired destruction 

 of charlock and runch. It must be remembered, however, 

 that these solutions were used on strong grown charlock. 



At no centre did the spraying have any injurious result on 

 the crops sprayed, which were oats, barley, and spring wheat ; 

 nor was there any difference observed in times of ripening. 

 In a few cases it was reported that after spraying the corn 

 became green, but this, it appears, applies to the portion 

 dressed with sulphate of iron rather than to those dressed 

 with sulphate of copper. 



In a few cases the crops were sprayed twice on the same 

 day, a plan which was found to answer well, and a double appli- 

 cation appears to be an advantage even if the solutions used 

 be somewhat weaker. When inspecting the experiments it 

 was noticed at many of the centres that a second batch of 

 plants had grown since the spray had been applied. A 

 second application after an interval of about ten days would 

 also have destroyed this second crop. 



In order to test the effect of the solution on other plants, a 

 number of pots were sown with various cereals, roots, grasses^ 

 and vegetables at the experimental farm at Garforth, and the 

 seedlings sprayed with a 1 2 per cent, solution of sulphate of 

 iron. The only plants seriously affected were beans, mustard, 

 turnips, and swedes. Of the last three, which all belong to 

 the same order as charlock and runch, the mustard suffered 

 much more than turnips, while the swedes suffered least. The 

 destruction of the beans was due to the large quantity of 

 sclution applied. 



In concluding his report on these experiments, Professor 

 Campbell observes that nothing certain is known with regard 

 to the specific action of sulphate of iron and sulphate of 

 copper solutions on charlock plants. It cannot, he thinks, 

 be due to the roughness of the charlock leaves retaining the 

 spray, for there are many other plants which retain the spray 

 equally well and yet escape injury. In all probability the 

 result is due to the fact that cruciferous plants contain 

 certain substances peculiar to their order, substances which 

 may react chemically with iron or copper salts. 



