Classificatiuii. j^g 



CHAPTER XXII. 



Classification. 



It is often hinted, or e\enly plainly stated, that the systematic classification 

 of Fungi is neither necessary nor useful where the object in view is to 

 investigate diseased conditions due to parasitic fungi. It is contended that 

 the physiology and not the morphology is the important thing, that if the 

 life-history is clearly traced and the abnormal conditions propeiiv studied, 

 nothing further is required for a correct diagnosis of the disease. This may 

 be true for isolated instances, but where the diseases of plants are compre- 

 hensively studied, and, particularly in a continent like Australia, where the 

 fungus-fiora is not as yet too well known, I consider it to be indispensable for 

 a proper appreciation of the nature and effects of the diseased conditions, 

 that the nature and affinities of the organisms causing them be definitely 

 known and defined if possible. As the President of the Field Naturalists' 

 Club of Victoria remarked in his annual address for 1907 — " In a new country, 

 until your objects have been collected in fairly large numbers, and dealt 

 with fiom a systematic point of view, it is difficult to see on what lines to 

 investigate the steps in their individual life-histories." In fact, until their 

 affinities are known, comparative study is impossible. 



In the first place, if the parasite should happen to be a new one, it will 

 be a guide in our investigations to know how it is related to other forms, as 

 well as its modes of reproduction and so forth. In the next place, if it is 

 not a new one, its exact determination will enable us to learn what is known 

 about its habits and history, and possibly serve as a guide to some method of 

 treatment. In the third place, when it has been determined and catalogued, 

 it will enable the future investigator readily to know when he is dealing 

 with the same disease, and afford him valuable hints in tracing its course. 

 In the literature of Plant Pathology one often meets with more or less 

 elaborate descriptions of diseases, such as a Wheat disease, a Potato disease, 

 or a Lily disease, without a clue to the definite parasite, and in such diseases 

 there is often a doubt as to the distribution of the disease, and where the 

 symptoms vary somewhat there is difficulty in deciding as to its identity. 

 When the smut of maize was first discovered in Australia, it was naturally 

 concluded to be the corn smut common in America, and named accordingly, 

 but when its systematic position was settled it was found to be quite a different 

 smut, and while in some cases the determination of the fungus mav not help 

 us much in the way of treatment, in others, where its nature and mode of 

 attack are known, it may afford a clue of considerable value. 



In short, there are at least four factors to be considered in the study of 

 any particular parasitic disease — (1) the organism which is parasitic upon the 

 plant, (2) the plant which is attacked, (3) the predisposing causes which have 

 favoured the entrance of the parasite into the plant, and (4) the mutual 

 reactions of plant and parasite. 



The members of this group of parasitic fungi are, as a ruli'. easily 

 recognised by the production of soot-like masses of spores, and wliilr these 

 may be formed in any portion of the host-plant, the special parts in which 

 they occur are usually constant for each species, and this is frequently the 

 ovary which is thereby completely converted into a mass of spores. The 

 reason for the ovary ])eing so often chos;Mi foi' this purpose is ]ii()i)al>]y owing 

 to its being such a splendid situation for the dissemination of the spores. 



