10 BULLETIN 1029, U. S, DEPARTMEXT OF AGEICULTL^EE, 



injury resulted to commercial seed held at this temperature for as 

 short a time as 5 minutes. At 50° C. the fungus was killed in 30 

 minutes with the small number of seeds used, but here, again, 

 some detrimental effect upon commercial seed occurred ; in fact, seed 

 injury was evident in somewhat milder treatments than those reported 

 by Norton (5), This is probably due to differences in the suscepti- 

 bility of individual seed lots. Soaking the seed in water before treat- 

 ment did not appear to be of any distinct advantage. At present, 

 hot- water treatment does not appear to be sufficiently superior to the 

 mercuric-chlorid treatment described later to warrant its recom- 

 mendation for general use. Further comparative trials, however, 

 should be made. 



MERCURIC-CHLORID SOLUTION. 



Solutions of mercuric chloric! were made by dissolving the chemi- 

 cally pure salt in distilled water. The treatments were all conducted 

 at room temperature, about 20° C. Four methods were used: (1) 

 Soaking the cabbage seed in the disinfectant without previous treat- 

 ment and rinsing once in clean water after removal; (2) soaking 

 in the disinfectant without previous treatment and allowing the seed 

 to dry without subsequent rinsing; (3) soaking in watar for one 

 to four hours before placing in the disinfectant and rinsing once in 

 clean water after treatment; (4) dipping the seed first in alcohol 

 for two minutes, then transferring to the disinfectant for the desired 

 time, and finally rinsing in clean water. Mercuric chlorid caused a 

 gradual reduction in the percentage of germination of seeds propor- 

 tionate to the length of soaking and the concentration of the solu- 

 tion. Injury to the germinating seedlings was characterized by tem- 

 porary' or permanent stunting of growth and varied amounts of 

 necrotic tissue extending back from the margins of the cotyledons. 

 The results of experiments with mercuric-chlorid solutions are pre- 

 sented in Table IV. 



With the first method (soaking in the disinfectant and linsing in 

 water) little injury resulted from a 30-minute treatment with the 

 1 : 500 solution, and practically none from less severe treatments. In 

 the case of one lot of imported cabbage seed of rather low vitality 

 (not cited in Table IV), considerable injury resulted from the 30- 

 minute 1 : 500 treatment, indicating that treatments as severe as this 

 should be used with caution. In the case of most lots of cabbage 

 seed, however, the soaking may be prolonged to one or two hours with 

 only slight injury, and at three hours only medium retardation 

 may be expected. These stronger treatments completely eradicated 

 the fungus in the case of the No. 4-18 seed. The fungus in the No. 

 1-19 lot appeared to be much more resistant to this chemical. 



