300 BOTAMCAL GAZETTE [april 



parallel is not fair, since the values are not commensurate, but it 

 serves to make the point that if such knowledge in medicine is 

 probably contributory to prevention, probably it is also con- 

 tributory in our science. 



Thoroughness such as is attained in human pathology is in 

 reality manifestly impossible for several reasons, one being the 

 large number of plant diseases. Each plant species, to an extent, 

 has its own fungous parasites; there are more than 40 listed for 

 the apple alone. There are, perhaps, between 300 and 400 really 

 significant, economic plant diseases, and to master knowledge of 

 these is a great undertaking which is far from realization as yet. 



* 



Parasitic diseases present two chief elements, the host plant and 

 the parasite. There is also, what is perhaps more important, the 

 interrelation between these two, and what is also very important, 

 the relation between these two and the factors of environment. 

 It is with the study of these 5 elementary factors that pathology 

 has to do. Large attention in the past has been given to the para- 

 site, and in many cases it is the parasite alone which has been 

 studied. Proportionately little study has been given to the rela- 

 tions existing between the host and the parasite, while the relations 

 existing between environment and host, and environment and 

 parasite, unquestionably of great significance, present a compara- 

 tively unworked field. 



I wish to call attention briefly to the types of problems that 

 exist under the above analysis. Perfecting and stabilizing of the 

 taxonomy and nomenclature of the parasites are of course of 

 fundamental value to pathology. The limitation of the families 



confe<;cpd1v artificial: the 



main 



ithin 



is really satisfying. To illustrate, the form genera Penicillium 

 and Coremium are separated by ordinal rank, yet a single culture, 

 dependent upon conditions, may give the characters of one or the 

 other. Ordinal questions occur regarding Meliola, Thielaiith 

 Fusarium. Actinonema, Helminthosporium, and many other genera. 

 Examples of problems in generic limitation are the Phoma- 

 Phyllosticta, the Septoria-Rhabdospora-Cylindros port urn, the Meli- 

 ola-Capnodiiim-Apiosporiiim-Antennaria questions. Within the 



