22 BULLETIN 453, U. S. DEPARTMENT OF AGRICULTURE. 



tatively separated from the advantage due to the control of parasites. 

 The sum of the results of the treatments in stimulating germination, 

 protecting the germinating seed from parasites, and in preventing 

 damping-off are all cumulatively expressed by the increase in final 

 stand in the treated over the untreated plats at the end of the season. 



INCREASED SIZE OF SEEDLINGS CAUSED BY DISINFECTANTS. 



At three of the nurseries where experiments were conducted for 

 several seasons it was found that there was a distinct increase in the 

 size of pine seedlings as a result of treatment with sulphuric acid. 

 Immediately after the seedlings come up, the only effect, when there 

 is a noticeable effect, is a decreased growth rate in the acid plats. 

 This effect later disappears, and during the latter part of the season 

 the seedlings normally grow faster in the acid plats than in the con- 

 trols or in plats treated with most other disinfectants. At the nursery 

 at Halsey during 1912 and 1913, seedlings were measured in five 

 experimental series, three of jack pine, one of western yellow pine, 

 and one of Norway pine. The average of all five shows that the acid 

 caused an increase in height of 37 per cent. 



At the nurseries in the Kansas sand hills and at Garden City acid 

 had a much more surprising effect. The results with western yellow 

 pine indicated a moderate increase in the first season's growth, in 

 agreement with the Halsey results, this increase being still distinctly 

 noticeable, at least at the sand-hill nursery, at the end of the second 

 year's growth. But with jack pine at these nurseries unexpectedly 

 large increases were secured. At both nurseries jack pine ordinarily 

 makes a slow growth during the first season. In plats sown in Novem- 

 ber, 1912, and treated with sulphuric acid early the following spring, 

 the average height of jack pine after a year's growth was found to be 

 more than three times that of the seedlings in the untreated plats. 

 The effect of acid treatment on the seedlings at the Garden City 

 nursery is shown in Plate II, figure 1 . At the Kansas sand-hill nurs- 

 ery, root systems as well as tops were examined. The increase in 

 root development appeared entirely commensurate with the increased 

 size of the tops. The air-dry weight of the tops at the sand-hill 

 nursery was 7J times as great in these acid plats as in the untreated 

 plats. 



It is not to be expected that the acid will result in increased growth 

 of any species in all soils, as the effect on growth is apparently due 

 not to direct stimulation of the conifers, but rather to the effect of 

 the acid on the soil. It is interesting to note that the only great 

 increases in growth have been found at the nurseries where the soil 

 water contained the largest quantities of acid carbonates. 



The economic value of a moderate increase in growth, such as 

 is secured at Halsey, depends largely on the system of handling stock. 

 If the seedlings are to be held in the seed bed for two years an increase 



