18 BULLETIN 169, IT, S. DEPAKTMENT OF AGKICULTUKE. 



to come up, but caused them to die a few days later. With the 

 weeds, nearly all that came up were quite certain to survive. The 

 extent of the injury to weeds was shown chiefly by the small number 

 of weeds which appeared on the acid plats as compared with the 

 checks. The failure of seriously injured weed seedlings to appear 

 above ground, as did most of the injured pines, may be due in part to 

 a larger amount of stored food material in the pine seed and in part 

 to a greater depth of soil over many of the weed seeds. It is barely 

 possible that many still dormant weed seeds were killed at the time 

 of the application of the acid. Some of the weed seeds in late-sown 

 plats commence germination at or before the time of acid application, 

 and are therefore probably killed at the time of application. The 

 frequent occurrence of healthy "Equisetum in beds where the acid 

 killed the pines may be due entirely to the presence of old rootstocks 

 and not to superior tolerance of acid. It has been suggested that 

 the survival of grass where acid prevented the appearance of dicoty- 

 ledons may be due to the branching habit of the grass roots, which 

 makes injury to the tip of the primary radicle of less importance 

 than with the plants which depend largely on a main taproot. 



Despite the qualifications in the preceding paragraph it seems 

 quite certain that a great many germinating weed seeds which were 

 dormant at the time of the application of the acid and were deeper 

 in the soil, and therefore exposed to lower concentrations of acid 

 than the pines, were killed in much the same way as the pines by 

 amounts of acid which would not injure the pines. The experiments 

 indicate not only a distinctly greater tolerance for sulphuric acid in 

 the pines than in the angiosperms most commonly represented in the 

 beds, but within the angiosperms a somewhat smaller difference in 

 tolerance between the grasses and dicotyledonous species was ob- 

 served. Tests in water culture would be necessary to establish the 

 differences in resistance of the various species observed in these 

 experiments and to give the differences a quantitative value. 



Treatments several days or weeks before sowing also had consider- 

 able effect on the number of weeds found in the seed beds during the 

 first few weeks after the germination of the pines. The use of 0.3 

 ounce of acid 14 days before sowing, with sufficiently frequent 

 watering after sowing to prevent injury to yellow pine, prevented 

 the appearance of any dicotyledons for at least 43 days after treat- 

 ment and allowed only a few grass seedlings near the edge of the 

 plat and a couple of Equisetum plants. Mollugo, grass, and Portulaca 

 seedlings were common in all the check plats in this series, and Ama- 

 ranthus and Euphorbia were present, while Equisetum was at least 

 no more common in the checks than in the acid plats. 



