196 BACTERIA IN RELATION TO PLANT DISEASES. 



that we want to increase the efficiency of the test, if we can, by the addition of some form of organic 

 matter, which will aid us in determining the real efficiency of disinfectants in the presence of organic 

 matter. This point is especially important in connection with disinfectants which act by oxidation. 

 If you try permanganate of potash on naked organisms you will find that it is very efficient, but if 

 you mix with it a little dust you will find that its power has largely gone down." 



Dr. Schryver in the discussion also cited the physical action of organic matter held in suspen- 

 sion as well as in solution and considered this to be important. 



GERMICIDAL TREATMENT OF SEEDS. 



Seeds with a thick impenetrable seed-coat offer no special obstacles to thorough dis- 

 infection. All that is necessary is actually to wet every part with a strong germicide for a 

 sufficient length of time. To insure this wetting there should be a brief preliminary wetting 

 in alcohol that air may be driven out of all the minute crevices where otherwise the germi- 

 cide would not penetrate. 



The case is quite different, however, with seeds having delicate and easily permeable 

 seed-coats. These have to be treated with great care, and often it is not possible to dis- 

 infect their surface thoroughly without at the same time destroying the embryo, at least 

 in a large proportion of the seeds. Sometimes in such cases we may reach the end desired 

 indirectly, i.e., by not allowing the seeds to become infected, since they are always originally 

 sterile inside the unopened pods. To obtain sterile seeds it is suggested that the unopened 

 seed-pods be collected with great care and their surface treated with germicides or fire, or 

 both, after which the pods must be carefully opened (in still air), and the seeds removed by 

 means of sterile forceps (see fig. 2, and p. 135) . 



The writer found that 15 minutes' exposure of hard dry kernels of sweet corn to i :iooo 

 mercuric chloride did not entirely sterilize the surface, although from the results obtained 

 it must have come very near to doing it, so far as regards the death of the organism in 

 question, i. e., Bacterium stewarti. 



Experiments made by the writer in the summer of 1909 with hybrid dent corns and 

 sweet corns having a high germinating capacity showed that the dry kernels would stand 

 exposure to i :iooo mercuric chloride water for 20, 30, 40, and 50 minutes with little injury, 

 the kernels being placed at once in damp sand after preliminary rinsing in hydrant water 

 or without rinsing. Nearly all germinated promptly and the seedlings looked as well as 

 those from the untreated seeds. 



In the first series twenty seeds were planted in each pot and the following are the 

 number of germinations per pot, the count being made on the sixth day: 



(1) U. S. P. B. No. ioo (field-corn): 



Checks, 20, 20, 20, 19, 19; Checks, none. 



Mercuric chloride (20 minutes), 18, 20, 17, 19, 19; Mercuric chloride (30 minutes), 18, 19, 18, 19, 20. 



In a second series of tests, using 20 seeds and counting on the fifth day, the follow- 

 ing results were obtained : 



(2) U. S. P. B. No. 120 (field-corn): 



Checks, 14, 18, 14, 17, 16; Checks, 16, 15, 17, 16, 18; 



Mercuric chloride (40 minutes), 18, 19, 15, 19, 12; Mercuric chloride (50 minutes), 18, 17, 16, 18, 20. 



There was no marked difference in the appearance of the seedlings. 



The experiments were repeated a few days later with this difference only, that the 

 seeds were not rinsed, but dried promptly and planted at once with the mercuric chloride 

 adhering to them. The results on the sixth day were as follows : 



(i) U. S. P. B. No. ioo (field-corn): 



Checks, 1 8, 20, 20, 19, 20; Checks, 18, 19, 20, 19, 20; 



Mercuric chloride (20 minutes), 19, 18, 16. 19, 17; Mercuric chloride (30 minutes) 18, 20, 19, 20, 19. 



The treated seeds showed a slight retardation in germination. Checks 2 to 3 inches 

 high ; treated i .5 to 2 inches high. 



