INJURY BY DISINFECTANTS TO SEEDS AND EOOTS. 



19 



In another series, in which watering was frequent enough to pre- 

 vent injury to most pine seedlings, 0.25 ounce of acid nine days before 

 sowing kept the plat free from all weeds except three grass plants for 

 1^ months, and 0.375 ounce applied at the same time prevented 

 weed growth of any sort. While grasses predominated in the un- 

 treated plats, they also contained many plants of Mollugo, Portulaca, 

 Amaranthus, and Euphorbia, their frequency being in the order 

 named. 



In another series watered in the same way, 0.281 ounce of acid 

 11 days before sowing and heavier treatments applied to three other 

 plats at the same time entirely prevented weed growth till 47 days 

 afterwards, while the checks contained the same species as those 

 in the former series. 



In series 519, plats A, C, and D (Table VI), 0.25 ounce of acid 

 had a distinct effect on the weed flora, practically the same as 

 0.375 ounce, in plats examined 66 days after application. 



In another series, watered quite frequently after sowing in order to 

 prevent acid injury, acid applied 14 days before sowing the pines 

 was tested. On adjacent plats the upper 6 inches of soil was par- 

 tially sterilized at about the same time by heating in a moist condi- 

 tion to above 80° C. in an oven, all parts of the soil being brought 

 to at least that temperature and kept there for not less than 10 

 minutes. The results are presented in Table IV. 



Table IV. — Weeds which appeared in plats disinfected by heat and by acid. 



Plat. 



Treatment (ounces 



of acid per square 



loot). 



Weeds found 42 days after treatment. 







60 to 100 per plat; grass commonest, Mollugo and Portulaca fre- 







quent, Amaranthus occasional. 



C 



0.25 

 .375 

 .375 

 .5 



2 or 3 Portulaca plants, and 1 Amaranthus in each plat. 

 5 grass seedlings, with several Mollugo near edge. 



F 



5 grass, with 1 Portulaca and 1 Mollugo near edge. 



G 



4 grass. 



D 



3 grass. 







Evidently, unless the grass seed survived a temperature of 80° C. 

 or more, it had been blown into plats J and K after treatment, and 

 migratory ability may explain part of its predominance over the 

 dicotyledons in acid-treated plats. The results in general, neverthe- 

 less, indicate that it is somewhat more resistant to acid than the 

 dicotyledons. 



RELATION BETWEEN TIME OF APPLICATION AND AMOUNT OF INJURY. 



The foregoing experience with pines and other plants in beds 

 treated with acid at the time of germination, at sowing time, and at 

 various times before sowing, shows clearly, as would be expected, that 



