Nov., 192 1 ] ENSIGN — ^ VEIN-ISLETS AS AN AGE DETERMINANT 
435 
ditions as possible were selected. Mature leaves from an unidentified 
species of grape (Vitis sp.) growing in the plant physiological greenhouse at 
Cornell furnished the necessary material. Only mature leaves were used, 
since it has been shown that the area of the vein-islets in immature leaves 
is much less than that in mature leaves. 
Portions of each of thirty-eight leaves from a single plant, having the 
same light exposure, were examined under the projection apparatus, as 
described in a previous article (4). The magnification used was thirty- 
eight diameters. A similar portion of each leaf was cleared and stained 
and determinations of the vein-islet area were made with the same apparatus 
and at the same magnification. Figure 3, Plate XXIII, shows the vascular 
tissue of the cleared and stained portion of this grape leaf. Table i shows 
Table i. Relative Size of Vein-islets of Uncleared and Cleared Portions of the Same Leaf 
(Vitis sp.) 
Number of Leaf 
Uncleared Portion 
Cleared Portion 
Vein-islets 
Hidden in 
Uncleared 
Leaves 
(percent) 
No. Vein- 
islets in 
Unit Area 
(4 sq. mm.) 
Area 
Vein-islets 
(sq. mm.) 
No. Vein- 
islets in 
Unit Area 
(4 sq. mm.) 
Area 
Vein-islets 
(sq. mm.) 
I 
14 
14 
21 
13 
18 
25 
17 
21 
15 
12 
16 
17 
.2860 
.2860 
.1904 
.3200 
.2222 
.1600 
•2353 
.1904 
.2666 
.3200 
.2500 
•2353 
30 
34 
33 
34 
35 
30 
33 
35 
30 
29 
29 
31 
.1333 
.1176 
.1212 
.1176 
•I143 
.1333 
.1212 
•I143 
•1333 
•1379 
.1379 
.1290 
54 
59 
37 
62 
49 
17 
48 
40 
50 
59 
39 
46 
2 
3 
4 
5 
6 
7 
8 
9 
10 
II 
12 
Average 
16.9 
.2468 
32 .1259 
47-5 
Mean Average 38 
Leaves 
i6.9±.i35 
.2485 
32 ±.263 
.1240 
47.5% 
a summary of the data obtained from this study. It is evident from this 
study that many vein-islets are invisible in the uncleared leaves even with 
a magnification more than twelve times as great as that used by Benedict. 
Indeed, the average shows that nearly half the vascular tissue is hidden by 
the chlorophyll, and in some leaves as much as sixty-two percent is invisible. 
On the other hand, some leaves show the major portion of their vascular 
tissue in the uncleared, unstained condition. 
Benedict (i) presents data which show that the vein-islets in uncleared 
leaves grown in the shade are smaller than those in leaves exposed to direct 
sunlight. These data interpreted in the fight of the experimental results 
shown in table I mean, no doubt, that the leaves grown in the direct 
