NATURE AND SYMPTOMS 9 



to the plant itself ; (h) by injuries to the leaves, inter- 

 fering with their activity ; (i) by malformations of 

 various parts of the plants. 



A disease may be of comparatively little importance 

 in the economy of the growing plant, but its injuries 

 may be of very great importance in the sale of the 

 plant products. Leaf spots may be of little importance 

 to the tobacco in preventing its normal functions, but 

 may reduce the market value of the leaf. Fruit rots 

 may not interfere with the growth and reproduction 

 of the plants, but may reduce or completely destroy 

 the commercial value, or prevent shipments to markets 

 which would otherwise be available. Other rots which 

 are practically unknown on the growing plants are very 

 destructive on stored plants. Still others (which are 

 not strictly the cause of diseases) attack seasoned 

 timbers and seriously interfere with its use for building- 

 purposes. 



The most common terms used in designating diseases 

 are : Rots, which attack fruits and other parts of the 

 plants, and are caused by fungi, bacteria, or unfavourable 

 soil and climatic conditions : they may be soft or hard, 

 wet or dry, odourless or offensive. Blights of the leaves, 

 stems, flowers, or fruits, which may be due to fungi or 

 bacteria : they may cause the death of part or all of 

 the plant, and may be followed by rots. Spots on the 

 leaf and fruit, usually due to fungi : on the leaves they 

 interfere with the normal functions of the plant and 

 the sale if it is of commercial value ; on the fruit they 

 cause discolorations and reduce the market value. 

 Scabs on fruit, leaves, and stems : they are usually 

 caused by fungi, and reduce the vitality of the plant, 

 sometimes causing death, or interfering with and reduc- 

 ing the market value of the fruits. Mildews, which are 

 always whitish, powdery, fungus growths on leaves, 

 twigs, and sometimes fruits : they may be partially or 

 entirely parasitic, and often the cause of heavy losses. 

 Burns on leaves and fruits, usually due to climatic 

 conditions, but frequently of great importance. Smuts, 



