168 
IOWA ACADEMY OF SCIENCES. 
connection with onr experiments on Long Island, they show 
that some varieties (notably Yellow Transparent) are wholly 
exempt from RoesteUa pirata and that there is good reason for 
believing that the absence of Boestelia 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. The 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 Boestelia. 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 Boestelia\ Maiden’s Blush and 
Wealthy contracted the disease readily and matured secidio- 
spores; on Ben Davis and Red Astrachan the Boestelia started 
to grow but never reached maturity; on Red Pippin, only part 
of the secidiospores matured. 
There are few fungous diseases of cultivated plants 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, Entomosporium maeula- 
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 Boestelia pirata^ 
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, Uromyces caryophyllinus (Schrank) Schroeter, perhaps 
most nearly approaches it. This rust is exceedingly destructive 
