DAMPING-OFF OF CONIFEROUS SEEDLINGS. 7 



The treatment finally adopted consists of three-sixteenths fluid 

 ounce of sulphuric acid per square foot of seed bed, applied in solu- 

 tion immediately after the seed is sown and covered. The amount of 

 water used to dissolve the acid varies from 1 pint per square foot 

 when the soil is wet to 2 pints when the soil is dry. In all disinfec- 

 tion of seed beds by chemicals the quantity of the disinfectant used 

 per unit area of soil surface seems to be the important variable. The 

 disinfectant must be dissolved in sufficient water to permit its dis- 

 tribution through the soil to a depth of several inches, but within 

 certain limits the concentration of the solution as applied does not 

 appear to be an important factor. The adherence of some investi- 

 gators to the concentration of the solution used as a measure of soil 

 treatment makes their work difficult to correlate. 



In the earlier tests of acid at Halsey chemical hi jury to the pines 

 occurred in beds treated with acid at the time of sowing. It was 

 found that dormant pine seeds were not injured by acid, but that the 

 root tips of the seedlings in acid beds were often killed just after 

 germination commenced. The way in which this injury occurred 

 made it evident that it was due to the concentration of the acid in 

 the surface soil. Evaporation of water from the soil surface seemed 

 to bring up the disinfectant from the lower soil, just as alkali salts 

 come to the surface in alkali soils. Watering the beds frequently 

 during the germinating period prevents such surface concentration 

 and in practice has been found entirely to prevent injury to the seed- 

 lings. The method of protecting the seedlings from acid injury at 

 this nursery is to water the seed beds frequently from the time seed 

 is sown until a few days after germination, when the root tips have 

 penetrated one-half inch into the soil. After this time they are prac- 

 tically safe from further injury. The beds are watered daily in ordi- 

 nary spring weather, every other day in misty or rainy weather, and 

 twice daily when the maximum temperature exceeds 80° F. In 

 clear weather each watering is at the rate of approximately 1 J pints 

 per square foot of bed. In cold, cloudy weather 1 pint per square 

 foot is found sufficient. (Two-tenths inch of rainfall is equivalent 

 to 1 pint per square foot.) 



The acid treatment was repeatedly tested on different species of 

 pine during different years and at different times of the year. In all 

 cases it resulted in increased stands. The results of all the acid tests 

 in which the above watering system or its equivalent was followed 

 are given in Table I. 



In addition to the three species given in this table, a test on a 

 series of plats of Corsican pine (Pinus laricio Poir.) gave excellent 

 results; an accident prevented the securing of exact figures. Some 

 of the tests included in the table were conducted on a considerable 

 scale, the total area involved being 8,350 square feet in the treated 



