SYMPTOMS OF DISEASE. 195 



the leaves, and the rendering useless of these areas 

 so far as providing further food-supplies is con- 

 cerned. The effects may be due merely to the 

 shading action of a parasite e.g: epiphytic fungi 

 or to actual destruction of the tissues invaded 

 e.g: by endophytic fungi or the tissues may be 

 burnt, poisoned, etc. In so far the results are 

 again quantitative and cumulative, and the amount 

 of damage depends on the number and size of the 

 spots or other areas affected, and the proportion of 

 foliage involved, as well as the length of time the 

 injurious action is at work. But, again, it must be 

 remembered that several symptoms may co-exist, 

 and matters may be complicated by the spread of 

 the destructive agent, or its consequences, to other 

 parts, and in some cases we are quite uninformed 

 as to the true nature of the disease. 



Notes to Chapter XX. 



Further information regarding these "leaf-diseases" will 

 be found in special works dealing with the fungi and insects 

 which cause them. In addition to works already quoted, the 

 reader may also be referred for Fungi to Massee, A Text- 

 book of Plant-diseases caused by Cryptogamic Parasites, 

 London, 1899 ; or Prillieux, Les Maladies des Plantes Agri- 

 coles, 1895. See also Marshall Ward, Cofifee-leaf Disease, 

 Sessional Papers, XVII., Ceylon, 1881, ^nAJoitrn. Lin7i. Soc, 

 Vol. XIX., 1882, p. 299. 



The question of" Sun-spots" has been dealt with by 

 Jonnson in Zeitschr.f. PJlanzenkrankh., 1892, p. 358. 



N 



