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 



