6 James Stew artv Wiant 



ment of the soil. A comprehensive discussion of this phase of control 

 may be found in the paper by Hartley and Pierce (1917) , who bring together 

 not only the results of their own extensive experiments but also the pub- 

 lished results of other investigators. Only the more important papers 

 dealing with the use of sulfuric acid, formaldehyde, zinc chloride, copper 

 sulfate, aluminum sulfate, and various mercury compounds, are discussed 

 here. 



Spaulding (1908, 1914), in experiments begun in 1905, devised the 

 sulfuric-acid treatment, while Hartley (1912 b) made the first extensive 

 tests with this material. Other publications by Hartley (1912 a, 1915), 

 Hartley and Merrill (1914), and Hartley and Pierce (1917), have shown 

 that of approximately fifty materials tested, sulfuric acid gave the most 

 promising results. Not only was the acid effective in controlling the 

 disease, but it reduced the number of weeds and caused increased growth 

 of the seedlings. However, it was ineffective in alkaline soils, and in some 

 nurseries caused chemical injury which necessitated frequent watering of 

 the beds during the period of germination and 'emergence. In a more 

 recent consideration of the original data, Hartley (1921) concludes that 

 the necessity for this frequent watering can be eliminated if in each locality 

 the minimum quantity of acid which will give reasonable control is 

 employed. Later reports on the use of sulfuric acid are those of Hansen 

 and others (1923), Tourney and Li (1924), Delevoy (1926), Wiant (1927), 

 and May and Young (1927). 



Early experiments with formaldehyde were made by Spaulding (1908, 

 1914), Jones (1908), and Gifford (1911). Hartley and his colleagues 

 (Hartley, 1912 a; Hartley and Merrill, 1914; Hartley and Pierce, 1917) 

 found formaldehyde effective, but less satisfactory than sulfuric acid. 

 Similar reports are made by Hansen and others (1923) and by Tourney 

 and Li (1924). The latter authors, as well as previous workers, noted 

 considerable reduction in emergence on the formaldehyde-treated beds. 

 Ma}' and Young (1927) reported that formaldehyde was superior to 

 sulfuric acid. From their published data it appears that under the same 

 conditions no treatment was made on more than a single plat. 



Zinc chloride and copper sulfate were found effective by Hartley and his 

 associates (Hartley, 1912 a; Hartley and Merrill, 1914; Hartley and 

 Pierce, 1917), and were recommended by them for use on alkaline soils 

 where sulfuric acid could not be employed. Hansen and others (1923) 

 also report tests with these two materials, but unfortunately these investi- 

 gators introduced a large number of varying factors into their experiments 

 without providing for numerous replications. 



Aluminum sulfate was successfully employed for the control of damping- 

 off of conifers under the direction of Hartley (Anonymous, 1926). Similar 

 results with this material were obtained by the writer (Wiant, 1927). 



Hartley and Merrill (1914) report unfavorable results from a limited 



