234 
Orton’ dealt with quite a different type of correlation when he reported 
in detail the similarities between six species of hetercecious Uromyces and 
six species of hetercecious Puccinia. He also extended this study to include 
autcecious 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 
zeciospores 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 
morpbological variacion 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 when a theoretical consideration of the condition is under- 
taken. 
The practical application of knowledge gained by correlation studies 
wiil be along the lines of culture work, especially in forecasting the alter- 
mate host plants of unconnected :ecial or telial forms. 
Mycologia, IV: No. 4, July, 1912. 
Purdue University, 
Lafayette, Ind. 
