Interspecific Transmission of Mosaic Diseases of Plants 7 



in the stem was effective. Subsequent experiments showed this method 

 to be less reliable, as well as more cumbersome, than the rubbing method. 

 As a rule, the instruments were disinfected after inoculation of each 

 plant. By this procedure, if one of the inoculated plants was already- 

 affected with mosaic without showing the symptoms, the disease would 

 not be carried from this plant to the others. In some cases in which 

 larger numbers of plants were used, the instruments were flamed only 

 after inoculation of two or three plants. In the earlier grafting experi- 

 ments, mosaic might have been carried from plant to plant by the razor 

 used in grafting; but later this danger was obviated by using safety- 

 razor blades and discarding the blades after they had been used on one 

 plant. 



RECORDS 



For the purpose of keeping records, all the plants of one species inocu- 

 lated with the same source of inoculum at one time were assigned a number. 

 Each plant was given a letter to distinguish it from the other plants of 

 the same experiment. The plants were examined almost daily, and a 

 record was kept of the first symptoms observed on each plant. 



DIAGNOSIS 



Ordinarily, no method of diagnosis was used other than the visual exami- 

 nation of the plants for symptoms. This method, of course, leaves some- 

 thing to be desired with reference to negative evidence. It is quite 

 possible for the symptoms of a mosaic on a given suscept to be so obscure, 

 at least under some conditions, as to escape detection; in such a case, 

 reinoculation of the original suscept from the plants in question would 

 show that they were carriers. It was unfortunately not found practicable 

 to carry out this method, mainly because the limited space available made 

 it impossible to keep on hand a constant supply of the necessary suscepts 

 in vigorous condition. 



It is possible also to err in the other direction, and diagnose as affected 

 by mosaic a plant which has been injured by fumigation, insects, or soil 

 conditions. There may have been isolated instances wherein this mistake 

 was made, but usually mosaic was not recorded unless definite and unmis- 

 takable symptoms were present. Extremely doubtful cases were omitted 

 altogether from the tables. 



Recognition and description of different mosaics 



As already mentioned, the different sources of inoculum produce dif- 

 ferent effects on the same suscepts. It is convenient at this point to 

 describe the symptoms produced by the different viri on the various 

 species used. In keeping the records of the experiments, it was found 

 desirable to record not only the presence or the absence of mosaic, but 



