19, 2 Lee: Citrus-canker Control 163 
placed the Tahiti lime (C. aurantifolia). In as much as all the 
other limes under observation were found to be highly suscep- 
tible, the relative freedom from c&nker of the Tahiti lime is very 
striking and should be taken advantage of in commercial growing. 
The species and varieties enumerated might be considered as 
class 2, all of which showed such a quick elimination of canker 
at the beginning of the control attempts that such measures 
would seem to be economically feasible. The Unshiu varieties 
known in America as Satsuma oranges (C. nobilis var. wnshiu), 
at least the Ikiriki, Owari, Zairai, Ikeda, and Wase, although not 
shown in these Lamao plats, from later experiments would also 
seem to belong in this class of susceptible but easily controlled 
fruits. 
A third class would contain many of the varieties of the sweet 
orange originating in Florida, such as the Pineapple, Homosassa, 
Magnum Bonum, Whittaker, and Parson Brown. This class of 
Sweet oranges is more susceptible than the varieties of the Medi- 
terranean group and would be more difficult to control. In this 
class would also be placed the Natsumikan of Japan and many 
of the pummelos, or East Indian type of C. maxima (grandis). 
Several of the strains of navel oranges would probably also be 
put in this class. The strains of the navel orange exhibit a 
considerable range of susceptibility; that is, some navel orange 
trees have been observed which were but very slightly affected, 
although exposed to infection for a number of years, while other 
strains, after exposure to infection for only one month, showed 
large percentages of affected fruits and foliage. The determina- 
tion of the susceptibility of these various strains of navel oranges 
is an important problem to be solved. To this class may be also 
added the Triumph grapefruit. The Triumph is the only variety 
that has been under observation which has shown any modifica- 
tion from the extreme susceptibility of the American-grown 
grapefruit varieties. It is by no means resistant, but its lesser 
degree of susceptibility to canker would perhaps make it of more 
value for commercial growing, and it might possibly serve as a 
basis for breeding toward resistance. 
Upon the varieties given above in what may be called the third 
class, it has been shown at Lamao that canker can be controlled. 
It is a question, however, as to whether this control is economic- 
ally feasible. The control obtained on these species and varieties, 
as has been shown, was obtained only after very careful pruning 
and a very large number of spray applications. The experi- 
ments have been continued in Japan and it is hoped that a report 
