28 BULLETIN 169, U. S. DEPARTMENT OF AGRICULTURE. 



erable injury to weeds, while in series 519, plat K, an amount 50 

 per cent greater, 34 days before sowing, with more frequent water- 

 ing, caused considerable injury to pines and had little effect on weeds. 

 Copper sulphate injured pines just as did the acids, by stopping 

 elongation of the radicles shortly after they emerged from the seed. 

 Recovery took place in many cases. A marked case of the production 

 of laterals in recovery from copper-sulphate injury is seen in a seed- 

 ling taken by Dr. T. C. Merrill from a bed in a similar soil at Garden 

 City, Kans., which had been treated heavily with copper sulphate at 

 sowing and again after germination (fig. 2). Normal yellow pine at 

 this age should have a single straight taproot going down at least 

 five times as far as the one figured and with relatively little develop- 

 ment of laterals. Ferrous sulphate (series 519, plat L) gave little 

 evidence of toxic action in the soil as compared with other substances 

 used. Further tests are necessary to give comparable data as to the 

 behavior of copper acetate in the soil and the effect of lime in pre- 

 venting injury by copper salts, the test made (series 514, plat P) 

 being insufficient. The results in series 518, plat N, indicate that 

 zinc chlorid is as dangerous to weed roots in this soil as copper sul- 

 phate, or slightly less dangerous. 



Mercuric chlorid in the amounts used acts differently from any of 

 the substances previously mentioned, in that it kills dormant "pine 

 seed in the soil at Halsey at the time of application. In series 519, 

 plat V (Table VI), the seeds which failed to germinate were taken out of 

 the soil and carefully examined, both with a hand lens and with a com- 

 pound microscope. No indication was found that they had ever com- 

 menced germination. The difference is presumably due to greater 

 penetrative power. Mercuric chlorid in the soil is injurious both to 

 the roots of seedling pines and to weeds in quantities, which in the 

 case of the other salts tested would have no effect. The addition of 

 common salt to the mercuric chlorid at the time of application 

 appears to increase the damage it does in the soil, possibly by delaying 

 the entire breaking down of the disinfectant until it has time to act 

 on the plants. (Compare 518-C and 519-U with 518-D and 519-V.) 

 The additional toxic effect could hardly have been directly due to the 

 0.188 ounce of common salt per square foot applied, since 0.2 ounce 

 of salt per square foot applied dry to a jack-pine bed three or four 

 days before sowing in an earlier series had no effect on the pines or on 

 the grass and Mollugo common in the series. The addition of sodium 

 chlorid also makes the disinfectant more convenient to work with by 

 greatly increasing the rapidity of solution. The addition to series 

 518, plat A, of an amount of air-slaked lime equal in weight to the 

 mercuric chlorid applied four days earlier prevented most of the 

 injury to weeds which occurred with smaller amounts of the chlorid 

 in plats not limed. 



