958 
Journal of Agricultural Research voi. xxiv. No. n 
unfolding leaves and twigs. These plants present a more or less scabby 
appearance throughout the season. 
Yuzu or Kansu orange is a plant native of North China; in fact, it 
grows farther north than any other Citrus. Like C. mitis, it is quite 
resistant to canker, but very susceptible to scab. It is rather peculiar 
that there are here two plants, one native to the tropics, the other to 
North China, both somewhat resistant to canker, but susceptible to 
scab under Gulf Coast conditions. Scab is found on the Kansu plants 
throughout the growing season. 
The Natsu-Mikan, possibly a natural hybrid similar to the tangeloes, 
has so far remained free from scab. The Naranja and Narute oranges, 
introductions from the Far East, are among the most susceptible plants 
in the field. These plants present an extremely scabby appearance 
throughout the growing season. 
As a rule, all trifoliate orange hybrids are attacked to some extent in 
the early spring, varying in intensity, and depending somewhat on the 
second parent. Thus, citrunshu, with Satsuma as a second parent, is 
more susceptible to scab than citrange with the common orange as the 
second parent. 
The citrange hybrids vary still more in their susceptibility to scab, 
ranging from slightly susceptible to very susceptible. The behavior of 
the citrangequat is extremely interesting. Kumquat, the second parent 
of this cross belonging to the wild relatives, is outside the range of scab 
susceptibility. However, when crossed with the citrange, the resulting 
hybrid is very susceptible to scab, and the plants are generaly scabby 
throughout the growing season in the field. On the other hand, it is the 
most proiuising canker-resistant hybrid that has yet been found. 
Limequat has so far remained free from scab. The orangelo and 
oranguma have also remained clean. The orangequat is a plant similar 
in many respects to the Satsuma. Thus, in the type of plant and its 
susceptibility tojcanker and scab, it behaves like the Satsuma. How¬ 
ever, why shoulcjl it equal the Satsuma in its susceptibility to scab when 
both of its parents have been so far reported free from scab ? Its suscep¬ 
tibility to scab must be closely related to the reaction of this plant to 
environmental conditions favoring scab attacks. 
The bigaraldin presents the opposite extreme in that no scab has been 
observed on this hybrid, although both its parents, the sour orange and 
calomondin, are very susceptible to scab. 
The mandarin orange-grapefruit hybrids as represented by satsumelo, 
clemelo, and tangelo vary from slightly susceptible to susceptible. No 
scab has been observed on siamelo. The hybrids having Citrus mitis as 
one parent either have remained free from scab or are only slightly 
susceptible, notwithstanding the fact that C. mitis/is very susceptible 
to scab. 
All the false hybrids vary from slightly susceptible to susceptible, de¬ 
pending on the condition of the plants. 
SUMMARY 
The range of Citrus plants susceptible to scab has been extended much 
beyond the few well-lmown groups of commercial varieties, heretofore 
reported. No doubt some of the plants reported as nonsusceptible may 
later be found to be susceptible, while many species and varieties which 
were not tested will also be found to be susceptible to scab. 
