INJURY BY DISINFECTANTS TO SEEDS AND ROOTS. 11 
tip of the root and the tissue just back of it is well shown by the 
location of the new laterals developed by the seedling in figure 1. 
In addition to the increased concentration of the acid solution 
already in the surface soil, due to the decrease of the solvent, acid 
from lower levels is presumably brought up to the surface by the 
capillary rise of the soil solution to replace that lost by evaporation. 
When the treated soil is soaked thoroughly with water and subjected 
to continuous evaporation for several days, but at a rate slow enough 
to avoid drying the surface soil entirely and breaking the capillary 
connection, this continuous upward movement of solution ultimately 
results in killing concentrations in the surface soil, even while it is 
still very moist. The problem of preventing injury to seedlings 
therefore becomes one of not only keeping the surface soil moist, 
but of maintaining a fairly constant downward movement of soil 
moisture, or at least of preventing a continuous upward movement 
for any considerable period, until after the roots of all seedlings 
have extended half an inch into the soil. Experience has shown 
that this can be done more easily with frequent light waterings 
than with heavier and less frequent applications. 
A very few hours' delay in watering at a critical time has in some 
cases been enough to cause the killing of root tips by acid. Under 
certain conditions, as outlined in the foregoing paragraph, injury 
occurred before the beds appeared at all dry at the surface. Since 
appearances could not be relied on to show when watering was 
needed, systematic watering was tested. Furthermore, variation in 
individual judgment made necessary the use of measured quantities 
of water. Daily waterings equivalent to 0.4 of an inch of rain 
were not in all cases sufficient to prevent injury entirely. However, 
half this quantity applied twice as often, with the soil wet to begin 
with, was found sufficient to prevent all injury from moderate 
amounts of acid, even in very hot, dry weather. For large beds at 
this nursery which have received 0.188 ounce of acid at sowing, 
watering equivalent to 0.3 of an inch twice daily during the germina- 
tion period has been recommended for summer use, so as to make 
certain that in the necessarily uneven large-scale work all parts of 
the bed will get at least 0.2 of an inch at each watering. 
For work in cold spring weather, when the germination period 
is long, the expense of this special watering becomes considerable, 
and it further cools the soil to such a point that germination may be 
still more delayed. No such frequent watering is necessary to 
prevent injury in cool weather, but because of occasional hot, dry 
weather in early spring it is not safe entirely to abandon watering 
twice daily. A rather extreme instance of the variable temperature 
at Halsey was the rise of the temperature, as shown by a Weather 
