Vol. 48 No. 4 
BULLETIN 
OF THE 
TORREY BOTANICAL CLUB 
APRIL, 1921 
A study of the structure of the stomata of two species of Citrus in 
relation to citrus canker 
Forman T. McLEAN 
(WITH ONE TEXT FIGURE) 
There have been many conjectures regarding the causes of 
differences in resistance of different plants to fungous and bacterial 
diseases. Usually these differences can not be correlated with 
any easily recognized characters of the plants in such a way that 
a definite character may be associated with the disease resistance. 
The stomatal structure, however, appears to yield such a character 
in certain of the species of Citrus in their relations to citrus canker 
(Pseudomonas citri Hasse). 
Marked differences have been observed in the various species 
and cultivated varieties of Citrus in their resistance to canker. 
Certain of the mandarin varieties, notably ‘‘Szinkum,” are very 
resistant, while grapefruit is highly susceptible, as clearly shown 
by Lee.* It has further been shown by Peltier} and by Leet 
that all species of Citrus and most of the related genera of Rutaceae 
can be successfully inoculated with canker by pricking the leaves. 
This seems to indicate that the resistant sorts that can be thus: 
* Further data on the Citrus canker affection of Citrus species and varieties at 
Lamao. Philippine Agr. Rev. 11: 200-2 g18. 
T+ Suscep sans and resistance to Citens canker of the wild relatives, Citrus 
fruits and hybrids of the genus Citrus. Jour. Agr. Research 14: 337-357- 1918. 
t Further data on the susceptibility of rutaceous plants to Citrus canker. Jour. 
15: 661-666. 1918. 
ie BULLETIN for March (48: 77-100. pl. 1) was issued March, 8, 1921.] 
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