122 The Philippine Journal of Science 1921 
leaves were fully exposed to sunlight, these differences may have 
been caused by variations in the rates of transpiration. 
TABLE 4.—Tests of pressure required to inject water into Citrus leaves, 
attached to twigs and standing in water, fully exposed to the sun before 
testing them. 
Width of ridge ot| 
entrance of stoma. 
1 Date. Hour. Kind of leaf. Pressure. . 
sein Average. 
a. M>-p.m. em. Hg. - & 
AML 7 ake 8. 26 Young Szinkom mandarin orange. 5.5 6.0 4.3 
aL | APPT 2-2. S0LBO Sc fea aus OG es ooo es ee eae 90.6 > les ca eee 
9A) ADTW 1 onus. Lape 2 Se eee NG 2 eo eaewae basa er 29.5 4.7 4.2 
Ble a | by cepa ae G10 tees 0 oo a case beteeee ose ya 5 ea RS ai ey gE a 
G4: ASTIL YT .<cc3.. 240) To G0 205 ca eenes poe es 17.0 7.0 4.1 
6:) Apr.T 2. 2c. 39 to Oto aa Soa seer ceca usaawoane SBF a eee ene 
With the small number of data presented, and these of such a 
highly variable character, it is obviously unsafe to make any 
more than the most general sort of conclusions. The effects of 
the different treatments employed appear to be quite evident from 
the foregoing comparisons of results. Less satisfactory con- 
clusions can be reached regarding the differences between the 
different varieties, and the possible correlation between the width 
of the ridge of entrance of the stoma and the injection pressure. 
Certain generalities are allowable from the data shown. Thus 
a consideration of the lowest values obtained, as shown in Table 
3, indicates that Pernambuco grapefruit is usually more easily 
injected than Szinkom mandarin, since of the five injection pres- 
sures below 5 centimeters four, including the two lowest values 
(2 and 5 millimeters), are for Pernambuco and only one (1.6 
millimeters) is for Szinkom. Further, the average injection 
pressure for Pernambuco is 7.9 centimeters, while for Szinkom 
(taken from the first three tables only, for those in Table 4 are 
not considered to be at all comparable to the others) it is 18.3 
centimeters. Likewise, the average width of the ridge of en- 
trance of the stomata of Pernambuco is 7.0 » and of Szinkom, 
4.1 ». Thus the average values for the two varieties indicate 
that Pernambuco grapefruit is more easily injected and has 
wider stomatal apertures than Szinkom mandarin. 
Another more extensive series of tests of the injection pres- 
sures of Citrus leaves is being made on leaves attached to the 
trees in the field, using a different technic. The results of these 
