INJURY BY DISINFECTANTS TO SEEDS AND ROOTS. 13 



In this series the variation between individual plats is great. 

 Especially in the cases of the 0.250-ounce and the 0.375-ounce plats 

 the variation between plats given the same acid treatments is much 

 greater than the average variation between plats given different 

 treatments or between the untreated plats, which are subject to 

 much heavier variation from the action of parasites than the acid- 

 treated plats. However, the averages indicate a distinct increase in 

 the amount of injury as the quantity of acid is increased. The great 

 individual variation between plats with the same acid treatment is 

 to be explained by two factors which were not controlled. In the 

 first place, different plats germinated at somewhat different times. 

 Some plats therefore had a much greater average root length than 

 others at the time the lolling concentrations of the soil solution 

 occurred. This greater root length resulted in the sensitive tip being 

 farther down in the soil, where the acid solution does not become as 

 concentrated as in the soil at the surface. It may also have been 

 true here, as found by McCool 1 in his work with barium, strontium, 

 sodium, and ammonium, that the root tips of seedlings a few days 

 old are less susceptible to injury than those of seedlings which have 

 just germinated, so that the age of the seedlings may have been even 

 more important than the location of the root tips in making the older 

 seedlings more resistant. Furthermore, those with the longer roots 

 were not only less likely to be injured but also had a better chance 

 to recover. (Compare PL I, figs. 3 and 4.) A more important 

 variable factor in causing different results in plats with identical acid 

 treatments was the watering during the germinating period. While 

 all plats were watered at the same time, no attempt was made in 

 series 501 to secure special uniformity in watering, and some became 

 drier than others. A later test of different amounts of acid was made 

 with plats sprinkled with measured quantities of water twice daily 

 during the germination period. Germination took place nine days 

 after the plats were treated and sown. The results are given in 

 Table III. 



Table III.— Relation of the amount of acid applied and the thoroughness of subsequent 

 waterings to the death of pine seedlings on plats treated with sulphuric acid at the time 

 of sowing. 



[Seedlings per square foot surviving 44 days after germination.] 



Water per square foot. 



Treatment (ounces of acid per 

 square foot). 



0.211 



0.250 



0.313 



2 pints at each watering seedlings . 



1.5 pints at each watering do . . . 



1 pmt at each watering do . . . 



281 

 125 



179 

 151 

 64 



142 

 91 

 47 



1 McCool, M. M. The action of certain nutrient and nonnutrient bases on plant growth. N. Y. Cornell 

 Agr. Exp. Sta. Mem. 2, p. 159-162, 1913. 



