Nature of Plant Diseases 103 



Cause of Mosaic. The cause of Mosaic is as yet 

 a disputed question.* AUard claims that mosaic is 

 caused by an ultra-microscopic pathogen, that is, a 

 parasitic organism which cannot be detected by our 

 present technic in microscopy. Mosaic may be 

 transmitted from plant to plant. The easiest way 

 to prove this is to rub with the fingers a diseased 

 leaf and then immediately rub a healthy one. The 

 disease will appear on the inoculated host in about 

 ten days. In the greenhouse, the green aphid and 

 the white fly act as carriers of mosaic. 



Control. Methods of control in mosaic lie in the 

 direction of prevention. Diseased plants should be 

 destroyed by fire, and all indoor insect pests kept in 

 check. 



* See also Taubenhaus, J. J., Truck Crop Diseases, E. P. Dutton 

 Co, 1918, New York, N. Y. 



