14 



BULLETIN 034, U. S. DEPARTMENT OF AGRICULTURE. 



cases. It may furthermore be that in other cases the disinfectant had 

 a stimulating effect, resulting in better germination in the treated 

 plats, entirely aside from that resulting from parasite control. The 

 number of disinfectant methods which concurred in giving apparent 

 increases in germination, however, makes it seem reasonably cer- 

 tain that no great part of the increase Avas due to this stimulation. 

 In addition to the different disinfectants shown in the table, mer- 

 curic chlorid, heat, hydrochloric acid, nitric acid, and ammonia all 

 apparently resulted in approximately the same increases of germina- 

 tion in tests at the Bessey Nursery as the sulphuric acid which was 

 used as the standard for comparison in most of the series. Relative 

 emergence in treated and untreated plats, as well as damping-off 



Fig. 7. — A clean-killed area in a bed of Pinus jionderosa, caused by Corticium vagam. 

 Inside a 12-inch circle at the center of this "patch" no seedlings appeared. It will 

 be noted that the weeds as well as the pines have been killed with the exception of 

 Balsola tragus. 



loss after the seedlings appeared, was determined at two nurseries 

 in addition to those given in the table. The results at these nurseries 

 in general confirmed those at the five nurseries covered by the 

 table in showing lower emergence in the controls. Although it is 

 impossible to draw positive conclusions, some idea of the seriousness 

 of losses before the appearance of the seedlings above ground can be 

 obtained by studying the data in Table I. The fact that such losses 

 appear considerable, sometimes exceeding the losses from the damp- 

 ing-off that occurs after emergence, is believed to explain the com- 

 mon failure to secure satisfactory results from control measures 

 taken after the seedlings have come up and the disease has become 

 noticeable. It is somewhat interesting to note that the data in the 



