The Rhizoctonia Damping-Off of Conifers 49 



White pine — Liquid treatments. An experiment was conducted with 

 liquid treatments of several mercury materials on beds of white pine at the 

 Keene nursery in 1926. Seed were sown on May 20 at the rate of 3000 

 to each plat. Since only about 25 per cent of the seed were viable, the 

 percentage of emergence was low. Field observations showed no evidence 

 of chemical injury at the time of emergence. Severe damping-off occurred 

 in the check plats, while practically none was apparent in the treated plats. 

 The data on final stand presented in table 16 demonstrate that nearly all 

 of the treatments were effective in producing from 200 to 400 more seed- 

 lings than were recorded for the check plats. The increases were for the 

 most part easily significant. 



It is interesting to note that in nine out of ten cases in which second 

 applications were made, the final stand was lower than for the correspond- 

 ing plats receiving but a single application. Field observations showed 

 that many seedlings were killed or stunted by the second applications of 

 mercuric chloride, while slight stunting occurred from second applications 

 of the other materials. Observations were repeated at the end of the 

 second growing season, and the plats were classified on the basis of the size 

 of seedlings contained in them. In class A are included those plats on 

 which the majority of the seedlings were of very excellent stock, in class B 

 those on which the seedlings were of fair size, and in class C those on which 

 the majority of the seedlings were of decidedly inferior quality and would 

 therefore normally be discarded. The average stock used for transplanting 

 at the Keene nursery ranges within the classes A and B, and is designated 

 by the combination A-B. Thus from the last column of table 16 it can 

 be seen that the smaller amounts of the materials, particularly where single 

 applications were made, gave the most promising results. 



