120 
The Philippine Journal of Science 
1921 
TABLE 2.—Tests of pressure required to inject water into Citrus leaves, 
detached from twigs and kept with their petioles in water in the 
diffused light of the laboratory for one-half day longer. 
Width of ridge ot| 
entrance of stoma. 
aut Date. Hour. Kind of leaf. Pressure. ve 
i Maxi- 
prone 45 Average. 
a.m, p.m, em. Hg, B Be 
10 | April 4 _-._--- 3.10 | Medium Washingtonnavelorange.| 21.5 9.7 7.8 
11-{ April 4°--.<-.- 8.85 | Half-grown Szinkom mandarin 
OFETNBOSS 28 os Sh ee 31.5 3.0 2.6 
12 | April 4 .._---- 4.10 |} Old, yellow Szinkom mandarin 
: OPbwE | cohol stoe chosen nce 31.0 6.3 4.0 
184 April 4 22.222. 4.50 | Old Pernambuco grapefruit_-_._- 6.9 10.0 9.0 
14 | April 4 ..._-.. 5.25 | Young Szinkom mandarin orange. SLE eas ae eae es 
20) Ape 6 ck 3.45 | Young Pernambuco grapefruit--- AY He pear a ow By 
16) ApEn T occ. 55 yA me |, Dees Meee 10: cikerbceaeat el edad. 9:5 tisce ea 
\ 13) Apel G25 yi eee Dee OG i iicektcctsmpastucusseame 14.0 y A) 4.7 
A comparison of the leaves of different apparent ages of the 
three different varieties showed no clear relationship between 
age and injection pressure. The individual variations between 
tests were so great that, in order to eliminate one possible 
variant, subsequent tests were confined to comparatively young 
leaves. Therefore, no conclusion can be drawn from these obser- 
vations concerning the effect of age of the leaves upon the 
injection pressure. All of the above tests show exceedingly 
variable and generally high injection pressures, probably due to 
the unfavorable conditions to which they were. subjected in the 
laboratory. 
Several tests were made on leaves which had been immersed 
in water and placed in the window in bright diffuse light previous 
to testing. The results of these are assembled in Table 3. Some 
of these were tested before placing them in the window, and 
are thus entered in Table 2. These repeated tests on the same 
leaves are particularly valuable for comparison and to show the 
effect of conditions of exposure on the leaf properties. 
The injection pressures shown in Table 3, in which the leaves 
were immersed in water and kept in bright light before testing, 
are génerally lower than those in Tables 1 and 2. Thus the 
values in Table 3 range from 2 and 5 millimeters in tests 23 and 
29 for Pernambuco grapefruit, to 15.5 and 18.0 centimeters - 
in tests 27 and 28 for Szinkom mandarin. Further, a compari- 
son of the same leaf, tested in each of the two series, is illuminat- 
