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IV. THE HORTICULTURAL PROBLEM. 



By F. J. CHITTENDEN, F.L.S., V.M.H., 



Director of the Royal Horticultural Society's Gardens. 



The subject to which I have to address myself is the method by which 

 the results of research into the causation and treatment of plant pathology 

 may be built into general horticultural practice, where the attacks of 

 bacteria and fungi upon cultivated plants growing under horticultural 

 conditions are concerned. 



In considering such a subject the mind naturally turns to a survey 

 of earlier attempts in this direction, and seizes upon what appear to 

 be causes of partial failure in the past; and it is largely upon this survey 

 that the remarks that follow are based. 



Both Professor Blackman and Dr Russell have traversed parts of the 

 ground which a full treatment of my subject should cover and it is 

 therefore unnecessary to enlarge upon points they have dealt with. 



In preparing their campaign of integration mycologists must re- 

 member that the problems involved are not only mycological, i.e., 

 belonging to an intimate study of the organisms involved. This study 

 cannot be too intimate and thorough, and it must include an enquiry 

 into the powers of adaptability possessed by the parasite, and also into 

 the range of variation existing or potential within its specific limits. 

 Besides this, the nature of the pathological conditions set up in the host 

 call for study. Further, as is well known, the incidence of disease in 

 plants is dependent to a great extent upon the temporary or permanent 

 environment of the crop, using the term environment in its largest 

 sense. Before mycological results can be thoroughly relied upon, the 

 conditions that favour, as well as those that discourage, the attack of 

 the parasite uj)on the host must be known, and the range of variation in 

 susceptibility to attack must be studied. Even with the commonest 

 diseases of plants our knowledge is only partial at present, and it would 

 tax the powers of tnost mycologists to the breaking point if they were 

 called upon to say whether such and such a method of apple-growing 

 would, with absolute certainty, avoid the incidence of even so well known 

 a disease as the common "canker." They could more easily say what 

 would conduce to the attack. 



The special problems of the mycologist are, therefore, part only of 

 the matter. The study of plant diseases in its entirety belongs really to 



