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 killing 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 x 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 
lpmt 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. 
