234 



Orton 1 dealt with quite a different type of correlation when he reported 

 in detail the similarities between six species of heteroecious Uromyces and 

 six species of heteroecious Puccinia. He also extended this study to include 

 autoecious species of Uromyces and Puccinia. In every instance the host 

 plants of the two rusts are of the same species, or of species closely related 

 morphologically and phylogenetically. Because of the cellular difference in 

 the teliospores (Uromyces. one-celled: Puccinia. two-celled) Orton laid 

 special emphasis on the agreement of the microscopic characters of the 

 jeciospores and urediniospores of the two rusts, remarking only in a gen- 

 eral way similarities between the teliospores. 



When we consider the differences in the number of spore forms in the 

 life cycles of the various species of rusts, and take into consideration the 

 morpnological variation of the analogous spores, it is apparent that the 

 possibilities of correlation are numerous. There are many problems pre- 

 sented in connection with such correlations. The choice of host plants, the 

 similarity of analogous spore forms, and the like effects on the host all 

 point to a common ancestor. What then is the primitive form? What is 

 the evolutionary history of the derivative species? How great a range 

 may be expected in the variations of correlated species? These and similar 

 questions arise wben a theoretical consideration of the condition is under- 

 taken. 



The practical application of knowledge gained by correlation studies 

 will be along the lines of culture work, especially in forecasting the alter- 

 nate host plants of unconnected secial or telial forms. 



! Mycologia, IV: No. 4, July, 191i 



I' urdu e University, 



Lafayette, Ind. 



