24 PROTECTION' OF PLANTS — 1922-23 



Symptomatology is another phase of plant pathology which is very imper- 

 fectly understood. In some cases we have the destruction of parts or all of a 

 plant, in others a dwarfing, in others an excessive growth, in others a wilting. 

 This may appear a simple problem but diseases, like the plants which are 

 attacked by them, are extremely variable. In fact so variable that a disease 

 which is very destructive in one part of the world may be so insignificant in 

 another part th^at its very existence may be denied. 



Bacteriology, that branch of botany which was not only alienated from the 

 mother science, but which became so closely affiliated with animal pathology 

 and other sciences is becoming more and more of a necessity for a well rounded 

 training in plant pathology. The honor of demonstrating bacteria to be one of 

 the causes of plant disease belongs to the New World. Dr. T. J. Burrill of the 

 University of Illinois in 1879 demonstrated that the pear blight was caused by 

 bacteria. Since then it has been demonstrated that many importajit plant 

 diseases are due to bacteria and I believe that I am safe in saying that North 

 America leads the world in this line of study. However, the probabilities are 

 that we have re;cords of a very few of a very large number of diseases due to 

 these organisms. Our knowledge of soil organisms, good and bad, in relation 

 to disease and crop production is very meager and presents a most fruitful 

 field for investigation. 



The methods by which diseases are distributed are not nearly so well known 

 as one would at first suppose. In a very general way we know that they are 

 carried on seeds, on nursery stock of various kinds, in packing materials, in 

 soils and manures, by wind and water, by birds, worms, snails and other ani- 

 mals. But the knowledge that certain mosaics are carried by insects and that 

 cucurbit wilt is carried by hybernating beetles has aroused us to a realization of 

 our own ingorance. In this connection, a study of zoology, especially entomo- 

 logy, becomes an important factor. Insects, nematodes, and other animal 

 organisms are both carriers and causes of many diseases and this line of work 

 must receive more attention from the pathologists. 



No one who is familiar with the broad field of plant pathology in its rela- 

 tions not only to the mother science — botany, but also in its relation to crop pro- 

 duction, transpoiHation of perishabltes and international problems, will ques- 

 tion the necessity for the most comprehensive training in the va,rious divisions 

 of botany and the related sciences, if the profession is to fulfil its obligations 

 to the public. Although the progress in plant pathology may appear remark- 

 able to the observer, the workers in the science know that the field is broaden- 

 ing and developing new relations unthought of by the founders of the 



