436 General Botany 



leaf development. The cause of the disease is not known. It 

 may be transferred to healthy plants by injecting juice from a 

 diseased plant. In the field it is apparently spread by insects. 

 Until the parasite is known and the exact manner of its transfer 

 from one plant to another has been discovered, control will be 

 impossible. 



Fig. 271. Mottled and crinkled leaf of potato afifected by mosaic disease. 

 (See also Figure 128, page 223.) 



