30 DISEASES OF TROPICAL PLANTS CH. n 



Kots, which are frequently very destructive to fruits 

 and vegetables, are due to many species of fungi and 

 bacteria which live partly parasitically and partly 

 saprophytically. These organisms are most important 

 on mature fruits and vegetables, attacking them at a 

 time when the cells are most dormant, and when the 

 contents are most suitable for fungus growth. Many 

 of these organisms cannot attack their host except 

 through wounds, while others have the power of 

 penetrating the uninjured surface. 



Many of the saprophytic fungi which attack and 

 destroy timbers of various kinds also have the power 

 of living parasitically on the growing timber. They 

 usually, probably always, gain entrance to the growing 

 trees through wounds, or start upon dead branches. 

 After living saprophytically for a time they gain 

 sufficient strength to penetrate the active, living tissues, 

 and frequently cause the death of the host plants. 

 These organisms are very destructive to forest, shade, 

 and orchard trees. The wounds may be caused in 

 many ways ; such as storms, rubbing together of 

 branches swayed by the wind, injury by animals, birds, 

 and insects of various kinds, lightning, sun scalds, and 

 by pruning. 



The action of some fungi upon plants reduces their 

 vitality and makes them more susceptible to other 

 diseases, or checks the growth of parts or of the entire 

 plants. Other fungi may stimulate parts of the plant, 

 causing the formation of galls, witches' brooms, etc. 

 While some fungi attack the leaves, others attack the 

 stems, causing cankers, and frequently causing the 

 death of all the parts beyond the point of attack. 

 Still other fungi attack the roots, injuring or killing 

 them, and thus resulting in a lowered vitality or in 

 the death of the plant. Still others attack the fruits, 

 and prevent their maturity or cause their decay. 



