DISEASE CAUSED BY FUNGI 197 



to be similar in every respect to those still attached to the 

 parent plant. Such experiments are undoubtedly instruc- 

 tive, and show the reciprocal influence of parasite and 

 host respectively under a given set of conditions, which is 

 perhaps as far as we are really justified in assuming. Pro- 

 bably every one will agree to the statement that plants 

 experimented upon, when grown under the conditions 

 enumerated above, are in that state which common ex- 

 perience has long ago proved to be the one most susceptible 

 to infection and disease. 



The only hope for a final solution of the intricacies 

 connected with diseases of plants caused by fungi, nay, of 

 disease in general, appears to depend on a fuller knowledge 

 of physiology and bio-chemistry. 



The knowledge possessed at the present day appears to 

 favour the idea that parasitism in fungi is an acquired 

 habit. This idea is supported by the cases recorded above, 

 also by the fact that the numerous fungi known as faculta- 

 tive parasites can live equally well either as saprophytes or 

 as parasites. 



It is not intended in this place to discuss the complicated 

 problem relating to disease ; those desiring information on 

 this point should consult Ward's masterly treatise on the 

 subject, entitled Disease in Plants. 



It is almost impossible to conceive any living organism 

 being placed under such conditions, that it is supplied 

 with all the requirements, and at the same time protected 

 against all harmful influences, necessary to ensure perfect 

 development. In proportion as a living body recedes 

 from this ideal condition, so its power of self-protection 

 may possibly, but not necessarily, become lessened, and 

 the influence of its departure from the mode of life normal 



