102 Diseases of Greenhouse Crops 



their role in human and animal pathology. Acting 

 as carriers of spores of parasitic fungi, which may 

 adhere to any part of their body, they are responsible 

 for distributing plant diseases. Insects, too, by feed- 

 ing on plants or in searching for the nectar of the 

 blossoms, are likely to come in contact with diseased 

 parts. Their bodies may become coated with spores 

 of parasitic bacteria or fungi, which are thus car- 

 ried from plant to plant and from field to field. 

 The striped cucumber beetle is known to carry the 

 virus of cucumber mosaic, and the germ of cucumber 

 wilt (Bacillus tracheiphillus Ew. Sm.). It is there- 

 fore very essential that every effort should be made 

 to keep insect pests out of the greenhouse. 



4. Diseases of Unknown Origin 

 Mosaic 



In this class will be included those diseases 

 which spread by contact, but the exact cause 

 of which is unknown. Special emphasis will be 

 given to that important disease known as mosaici 

 This trouble attacks a variety of greenhouse plants. 

 It is especially severe on the tomato, cucumber, and 

 sweet pea. 



Symptoms. Mosaic is readily distinguishable by 

 a yellow dotting or mottling on the foliage, present- 

 ing in some instances a beautiful mosaic structure, 

 whence its name. Affected leaves linger and often 

 curl. 



