168 IOWA ACADEMY OF SCIENCES. 



connection with our experiments on Long Island, they show 

 that some varieties (notably Yellow Transparent) are wholly 

 exempt from BoesteUa jnrata and that there is good reason for 

 believing that the absence of BoesteUa from cultivated apples in 

 Iowa is not due wholly to unfavorable climatic conditions, but 

 chiefly to the fact that the varieties grown there are not 

 susceptible to the disease. Tne severe climate of this section 

 has obliged orchardists to abandon all except the most hardy 

 varieties. These are mostly either Russian varieties or vari- 

 eties which have originated in the northwest. However, the 

 fact cannot be overlooked, that Wealthy, a variety shown by 

 our own experiments to be very susceptible on Long Island, is 

 frequently planted in Iowa, Wisconsin and Minnesota and is 

 there exempt from BoesteUa. We have by no means a com- 

 plete solution of this problem. 



In the Long Island experiments it is interesting to note that 

 while some varieties showed themselves wholly exempt and 

 others were very susceptible, there were also varieties which 

 presented intermediate degrees of susceptibility. Yellow 

 Transparent showed no signs of BoesteUa; Maiden's Blush and 

 Wealthy contracted the disease readily and matured secidio- 

 spores; on Ben Davis and Red Astrachan the BoesteUa started 

 to grow but never reached maturity; on Red Pippin, only part 

 of the secidiospores matured. 



There are few fungous diseases of cultivated i^lants which 

 are equally distructive to all of the varieties of the species 

 which they attack. Usually some varieties are much more 

 severely attacked than are others. Some varieties may be but 

 slightly affected, while others are ruined. Observant fruit 

 growers know that Flemish Beauty " scabs "-worse than most 

 other varieties of pears, while the fungus which produces the 

 leaf-blight and cracking of the pear, Eiitomosporiuiii macula- 

 tum, Lev., has a preference for the variety White Doyenne. 

 Wheat growers know that some varieties of wheat are more 

 liable to rust than are others. These are but a few examples. 

 Many more might be mentioned. In the case of BoesteUa inrata, 

 this preference for certain varieties is carried to the extremes. 

 We know of no other fungus which attacks some varieties of a 

 species so severely and yet cannot even be inoculated upon a 

 large number of other varieties of the same species. Carnation 

 rust, Uronujees caryophylUnus (Schrank) Schroeter, perhaps 

 most nearly approaches it. This rust is exceedingly destructive 



