Interspecific Transmission of Mosaic Diseases of Plants 31 



I noculations from potato 



In addition to the data presented in tables 2 to 22, some interesting 

 results were obtained by inoculating various plants with material obtained 

 from potato. These results seem to require special consideration. At 

 various times Nicandra Physalodes and Nicotiana glutinosa plants were 

 inoculated with leaves from potato plants which were affected with mosaic 

 A. Almost invariably these inoculations gave positive results, although 

 it was found impossible to secure infection with mosaic A when material 

 was taken from species other than potato. At first these positive results 

 were considered as evidence of contamination, but the consistency of the 

 results appeared to indicate some other cause. As a check on these results, 

 inoculations were made with supposedly healthy potatoes. Positive results 

 were obtained also in these cases. To check up on this unexpected develop- 

 ment, more extensive inoculations were made. More than a hundred 

 tubers of the Green Mountain variety were used, and the freedom of the 

 potatoes from mosaic was checked by planting the tuber remnants in 

 tuber units out of doors. The results were practically always positive. 

 The data on these inoculations are given separately in table 23: 



TABLE 23. Inoculations with Solanum tuberosum 



Species inoculated 



Nicandra Physalodes . . . 



Nicotiana glutinosa 



Solanum aculeatissimum 

 Datura Stramonium 

 Nicandra Physalodes . . . 

 Nicotiana glutinosa. . . . 



Type of 



symptoms 

 on potato 



A 

 A 

 A 



None 

 None 

 None 



Number 

 of plants 

 inoculated 



18 



8 



2 



4 



55 



60 



Number 



of plants 



showing 



symptoms 



16 



6 



2 



4 



46 



59 



Type of 

 symptoms 

 observed 



* The plants appeared to be a.fe^ted with a mixtare of mosaics A ani B. 



These results are strikingly similar to those recently reported by Johnson 

 (1925). Their exact significance is not clear. Two theories have been 

 suggested to account for this phenomenon. According to one theory, 

 the protoplasm of the potato acts as a pathogene and enters into a kind 

 of symbiotic relation with the protoplasm of the new suscept. This 

 theory is attractive because it suggests an explanation of the etiology of 

 mosaic diseases. The alternative theory is that the potatoes used actually 

 carried a virus; that is to say, they had mosaic although they appeared 

 to be healthy. Schultz and Folsom (1923) have shown that potatoes 

 are subject to at least three mosaics which differ in the readiness with 

 which they can be detected. It is well known that even the more pro- 



