6 



Karl Hermann Fernow 



Sph't-xtcm method 



In a few experiments, a slit was made in the stem of the plant to be 

 inoculated, and crushed mosaic leaf tissue was inserted. Flamed instru- 

 ments were used. This method, however, was found less effective than 

 rubbing. 



Grafting 



When other methods fail, positive results may sometimes be obtained 

 by grafting. This method was used especially with potatoes. There 

 are, however, several drawbacks. The method is laborious; the scion 

 often fails to live, and, even if it does live, it usually makes but little growth; 

 inoculum carried on the hands or on the knife may be accidentally intro- 

 duced; furthermore, only those species can be grafted which are closely 

 related. The procedure found most satisfactory was that known as 

 bottle grafting (Blakeslee and Farnham, 1923). This is essentially in- 

 arching, the lower end of the scion being placed in a shell vial containing 

 water to prevent drying out. 



Comparison of different methods 



It was soon found that the methods involving touching the plants with 

 the hands were unsatisfactory because inoculum was thus carried from 

 one experiment to the next. This is well shown in a series of experiments, 

 the results of which are given in table 1. Mosaic material was handled 

 or was placed on the instruments prior to the treatment of each plant. 

 The hands or instruments were then disinfected and the healthy plant 

 was inoculated with its own leaves. The results would seem to indicate 

 that, of the methods of disinfection tried, the flaming of instruments 

 was the only dependable one. The results would seem to indicate also 

 that the method of inoculation involving the placing of inoculum in a slit 



TABLE 1. Inoculation of Tobacco Plants by Different Methods 



