INJURY BY DISINFECTANTS TO SEEDS AND ROOTS. 17 



siderable quantities for the first two or three weeks, after which time 

 the number which came up decreased. 



Most of the data on the effects of sulphuric-acid treatments on 

 weeds were obtained on beds treated at the time of sowing. The 

 observations indicated marked differences between the species 

 observed in their ability to grow in soil recently treated with acid. 

 It was evident throughout that the pines were less easily injured than 

 most of the weed species. On plats which received no special water- 

 ing till after germination, 0.125 ounce and 0.141 ounce of sulphuric 

 acid per square foot, respectively, at the time of seeding entirely 

 prevented weed growth. The untreated plats in this series were 

 fairly well covered with Portulaca and grass species and with a few 

 plants of Amaranthus. At sowing in another series on a plat given 

 very frequent watering, 0.125 ounce of acid failed to reduce per- 

 ceptibly the number of common weeds. Another plat given the same 

 treatment, which had also received 0.125 ounce of acid 13 days before 

 sowing, showed entire freedom from weeds, with only partial injury 

 to the pines. In repeated tests during successive seasons, treatments 

 of 0.188 ounce of acid at the time of sowing regularly prevented 

 practically all weed growth for the first three weeks after the germi- 

 nation of the pines. In some cases no weeds came up in treated beds 

 until a month after the appearance of the pines. Beds treated with 

 acid and so watered as entirely to prevent injury to the pines were 

 nevertheless so free from weeds as a result of acid application that 

 the cost of weeding the treated beds during the whole season has 

 been only one- third that of untreated beds. 



The appearance of Equisetum in acid-treated plats was of some 

 interest. In an insufficiently watered acid plat on which the pines 

 were seriously injured and on which not a single phanerogamic weed 

 appeared, more Equisetum developed than in most of the untreated 

 beds in the nursery. Equisetum was not a common weed anywhere, 

 but it occurred more frequently in the acid beds than in the beds not 

 treated. 



The grasses throughout gave evidence of greater ability to endure 

 the acid applied to the soil than did the dicotyledons. They were 

 usually the predominant weeds and often the only ones in acid plats. 

 This greater predominance of grasses over dicotyledons in the acid 

 plats left little doubt as to their superior endurance of this treatment. 



Unfortunately, few data were secured as to the factors which con- 

 trolled the varying capacity of the different plants observed to 

 endure acid applied to the soil. Most of the injury to the weeds did 

 not occur in just the same way as to the pines. In the pines the 

 commonest phenomenon was root injury, which allowed the seedlings 



71222°— Bull. 169—15 3 



