REPORT CiF THE SOCIETY 25 



Many of our most serious diseases are due to fungi which live on more than 

 one host plant, some of them having different stages which are very unlike. 

 The wheat rust living on both the wheat and barberry, the white pine blister 

 rust living on both the white pine and the currants and the apple rust living 

 on both the apple and the cedar are well known examples of such fungi and there 

 are no doubt many others that are unknown to us. 



While it is true that in some cases we have been able to give successful 

 treatments for certain diseases Avithout knowing the life history of the parasite, 

 it is also true that we have failed in many cases until this information was ob- 

 tained. It is also true that many of our treatments have been improved as a 

 result of increased knowledge of the history of the parasite. In reviemng the 

 efforts at preventive measures for a period of more than 100 years we find that 

 sulphur was frequently used with varying and uncertain results, partly because 

 the workers of that time did not know how to prepare and apply it and partly 

 because they did not understand the causal organisms. In fact in many cases 

 they were ignorant of the presence of a parasitic organism. When practically 

 all cereal smuts were known as Ustilagocarbo, the results of the treatments were 

 very uncertain, but when the species were separated and their life histories 

 known, successful treatments were developed very rapidly. 



Plant physiology is essential to the training of the plant pathologist be- 

 cause a diseased plant is one in which the physiologica,! reactions are disturbed, 

 regardless of cause; and because the plant pathologist is endeavoring to grow 

 normal plants, i.e. plants in which the physiological disturbances are reduced to 

 the minimum. A knowledge of plant nutrition was necessary for the develop- 

 ment of plant pathology and an increased knowledge of this subject, of soil 

 toxins, of enzymes, and of filterable and non-filterable viruses will prove the 

 stepping stones of much of our future progress. Much of our culture work, 

 our studies on physiological species, resistance to diseases, change in soil, mois- 

 ture, temperature, and water levels will depend on our knowledge of plant phy- 

 siology and ecology. De Bar}^ was the first to clarify our idea concerning the 

 relationship of parasite and host and although this has been the subject of con- 

 siderable study, our knowledge of the exact physiological relationship between 

 these two groups of organisms is e'xtremely limited. In some cases the parasite 

 is general, spreading throughout the entire plant, while in others it is restricted 

 to obtain organs or parts or organs. In some cases there is a clogging of water 

 passages resulting in wilting, in others the excretion of poisonous substances, 

 in others the absorption of water and food, and in others the dissolving of pajt 

 or all of the cell wall. 



