CHAPTER XIII. 



NATURE OF DISEASE. 



General and local disease General death oiving to cutting- 

 off supplies, etc. Disease of organs Tissue-diseases, 

 e.g. timber Root-diseases Leaf-diseases, etc. Dis- 

 eases of Respiratory, Assimilatory, and other organs 

 Physiological a?id Parasitic diseases -Pathology of 

 the cell Cuts Cork Callus Irritatiofi Stimula- 

 tion by protoplasm Hypertrophy. 



On going more deeply into the nature of those 

 changes in plants which we term pathological or 

 diseased, it seems evident that we must at the out- 

 set distinguish between various cases. A plant 

 may be diseased as a whole because all or practi- 

 cally all its tissues are in a morbid or patho- 

 logical condition, such as occurs when some 

 fungus invades all the parts or organs e.g. 

 seedlings when completely infested by Pythiiim, 

 or a unicellular Alga when invaded by a minute 

 parasite ; or it may die throughout, because some 

 organ with functions essential to its life is 



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