DAMPING-OFF OF CONIFEROUS SEEDLINGS. 21 



seed bed for a second year run from four to ten times this figure. If 

 the minimum stand commonly desired, i. e., 100 seedlings per square 

 foot, is obtained on untreated beds, an increase in stand of only 20 

 per cent will mean an increased production of 20,000 seedlings, of a 

 minimum value of $10 for the 1,000 square feet taken as a unit. 

 Even in this minimum case, therefore, the treatment may be con- 

 sidered to have paid for itself twice over. The ordinary net results 

 should be still more favorable, for the following reasons: 



(1) At nurseries where acid or copper sulphate can be used without especially 

 frequent watering the cost of the treatment will be less than at Halsey. At only 

 one other nursery has it been found necessary to water the treated beds as much as 

 at Halsey. 



(2) The average increase in stand resulting from the treatment is much greater 

 than the 20 per cent used in the preceding calculations. Figures based on exact 

 counts for two or more seasons are available from five localities (Halsey, the Kansas 

 sand hills, Garden City, Fort Bayard, and Monument). The average increase in stand 

 resulting from the best treatments at all of these nurseries is exactly 100 per cent. 



(3) An additional advantage, of greater value than the average increase in stand, 

 is the stabilization of output through the prevention of damping-off epidemics. 



(4) A further advantage is the development of more uniform stands in the beds by 

 the prevention of damping-off patches. 



(5) In addition to the advantages from increased stands and decreased damping-off, 

 disinfectant treatment often has incidental results in the way of weed control or of 

 increased growth of the conifers which may by themselves more than pay all costs 

 connected with the treatment. These secondary advantages are discussed in the 

 following paragraphs. 



SECONDARY ADVANTAGES FROM DISINFECTANT TREATMENTS. 



STIMULATION OF GERMINATION CAUSED BY DISINFECTANTS. 



It is common and, in fact, almost invariable with all of the disinfect- 

 ant treatments which have been successfully used to find a higher ger- 

 mination percentage in the treated plats than in the controls. In 

 some cases this increase in germination (or, more accurately speak- 

 ing, in the number of seedlings which appear above the soil surface) is 

 very large. Whole groups of treated plats have in some cases given 

 an apparent germination percentage three times that prevailing in 

 the untreated plats in the same group. While such large increases 

 are not common, it is a very frequent thing for the advantage in 

 increased germination to be greater than that resulting from the 

 control of damping-off after germination. (Compare the first and 

 second columns under the head of "Relative results" in Tables I 

 and II.) Such increases are mainly due to the control of parasites 

 by the treatments; in the untreated plats Pythium and Rhizoctonia 

 kill many seedlings or sprouting seeds before they break through the 

 soil cover. However, in some cases at least, disinfectants, by direct 

 action or by their effect on the soil, appear to cause seed to germinate 

 which would otherwise have remained dormant. The advantage 

 from, this apparent stimulation of dormant seed can not be quanti- 



