338 The Philippine Journal of Science 1922 
into the season than the navel orange, in this district. These 
experiments were also carried on in Nagasaki Prefecture, Japan. 
The technic, sources of inoculum, and maintenance of inoculated 
fruits were the same as for the Washington navel fruit inocula- 
tions. The results are recorded in Table 4. 
Stomatal infections obtained on the Unshiu orange fruits are 
shown in Plate 4. It is apparent from the results in Table 4 
that there is a period during which Ikiriki Unshiu orange fruits 
have a considerable degree of susceptibility. Similar experi- 
ments were carried on upon the Owari Unshiu orange, the Zairai 
Unshiu orange, and the Wase Unshiu orange, in which the 
susceptibility varied but little, but in which the period of 
susceptibility was somewhat shorter than in the case of the 
Ikiriki orange, usually not more than seventy days. There is 
apparently a much shorter period of susceptibility in the case 
of these varieties than is the case with the Washington navel 
orange. The total period of possible infection is not more than 
ninety-eight days for the Unshiu oranges, as compared with one 
hundred fifteen to one hundred twenty days for the Washington 
navel orange. 
There are further but less systematic data which point to a 
longer period of susceptibility for fruit tissues of the grapefruit 
[Citrus maxima (decumana)] than for either the Washington 
navel orange or the Unshiu orange. The differences in length 
of the periods of susceptibility of these species is well illustrated 
in the graph, fig. 1. 
Age of fruit at time of inaculgtion; days. 
60 75 390 K 
5 30 45. 05 RB 5 
Stomatal | 
Ss 
numerous, . a 
Puncture | ™. os es 
dnfections 100 % 2 oe Be i 
Stematal : ty PA 
infections | PN. ion, Beg 
ew, + =z 
g Puncture S es, og 
‘3 | infections 100 %. is oa NS, 
& No stomatal 
= J infections 3 
% Puncture 
g infections 100%. * 
\S 
Ss % 
et } \ ers 
few, 2 ae | : 
Wo 1 ae o 
. infection J 80 
Fic. 1. Graphs showing the differences in lengths of periods of susceptibility of three com~- 
mercial citrus varieties. The line of the period of susceptibility of the grapefruit 
varieties is not based on actual ages of the fruits, but the estimated ages judged 
by their sizes, 
€ 
