Presidential Address. F. T. Brooks. 27 



the serious study of disease in plants. Just as plant physiology 

 is dependent in part upon systematic botany, so is a knowledge 

 of the fungoid diseases of plants dependent upon systematic 

 mycology for accurate treatment. Whenever one branch of 

 knowledge is intimately connected with another there is usually 

 a mutual reaction of the one upon the other and I trust that 

 plant pathology wdll be not without influence on systematic 

 mycology. Persons who investigate plant diseases often en- 

 counter "difficulties in the identification of the pathogen which 

 can only be solved with the aid of the systematic mycologist, 

 and I should like to acknowledge here the great assistance 

 received in my own work from systematic mycologists. But 

 the plant pathologist is often avaricious in his desire for in- 

 formation, and sometimes the particular knowledge he requires 

 from the systematic mycologist is not at present available. The 

 plant pathologist is accustomed to growing pathogenic fungi 

 in Dure culture whenever possible, where their behaviour can 

 be followed under carefully controlled conditions. In this way 

 he gets an idea of the range of variability of a species which is 

 often at variance with its formal diagnosis and with that of 

 allied forms. Thus the innumerable forms of Cladosporium which 

 have been described in systematic works are meaningless to 

 the plant pathologist, for he finds by experience that they can 

 all be grouped around a few types which are the real units. 

 It is clear that species must be diagnosed upon the basis of 

 characters shown on natural substrata, but the time has come 

 when these descriptions should be supplemented by an accurate 

 account of their behaviour upon standard media under con- 

 trolled conditions wherever the forms can be readily cultivated. 

 To diverge for a moment; this mode of treatment has become 

 an urgent necessity for the moulds as sho\\Ti by Thom in the 

 genus Penicillium and by Lendner in the Mucorineae, and the 

 time can be foreseen when biochemical reactions will be of 

 fundamental importance in differentiating such types. It may 

 be remarked that it is merely a platitude to urge supplementary 

 descriptions of the species as grown in artificial culture, but it 

 is important to reiterate this necessity, for few systematic 

 mycologists yet realise its significance. 



Again, with parasitic genera like Ramularia, Ovularia, Gloeo- 

 sporium, etc., the diagnosis of species is unsatisfactory to the 

 worker on plant diseases. The chances are that if either of these 

 forms is found on a new host, a new species will be created 

 without adequate comparison with existing species. Shear and 

 Wood* have shown that many species of Gloeosporiiim hitherto 



* Shear, C. L. and Wood, A. K., Studies of fungous parasites belonging to the 

 genus Glomerella. U.S. Dept. Agric, Bureau of Plant Industry, Bull. 252 (1913). 



