VENATION AND SENESCENCE OF POLYEMBRYONIC CITRUS PLANTS 3I9 
Influence of the Maturity of the Leaves upon the Size of the 
Vein-islets in Citrus grandis 
There seem to be no data published concerning the duration of time 
that the leaves persist upon grapefruit plants. Some of the plants at the 
greenhouse are now three years of age and no appreciable leaf drop has been 
noted. A leak of illuminating gas defoliated some of the plants of other 
species in this house, but the injury, if any, to the grapefruit was not 
sufficient to be noticeable. New growth is terminal and begins in the 
greenhouse early in March following a rest period. 
In some of the preliminary work, which was done during the summer of 
1916, it was noted that among five or n^ore leaves taken from a single plant, 
one or sometimes two would occasionally show vein-islets very much smaller 
than those in the other leaves. In order to determine the meaning of this 
discrepancy the following method was employed. Beginning with the 
topmost leaf and proceeding downward to the last leaf at the base, a series 
of leaves was taken which represented the oldest and youngest leaves upon 
the plant and a gradual gradient from one to the other. In most cases 
sixteen leaves comprised such a series, and their individual venation was 
determined. Table 5 gives the data from one series. The others were all 
'comparable with this one. 
Table 5. Variation in size of vein-islets in leaves of Citrus grandis owing to different degrees 
of maturity 
Leaf No. 
Diameter of Leaves Mm. 
Short 1 Long 
No. Vein-islets per Unit 
Area (4 Sq. Mm.) 
Size of Vein-islet 
(Sq. Mm.) 
I 
8 
23 
103 
.0388 
2 
10 
28 
98 
.0408 
3 
II 
30 
72 
•0554 
4 
18 
36 
67 
•0597 
5 
24 
50 
54 
.0741 
6 
32 
60 
41 
.0975 
7 
39 
80 
27 
.1483 
8 
30 
70 
20 
.2000 
9 
48 
no 
13 
.3123 
10 
45 
82 
12 
•3333 
II 
20 
35 
II-5 
•3499 
12 
40 
70 
10.8 
.3860 
13 
30 
55 
9 
.4500 
14 
35 
50 
9.5 
•4730 
15 
30 
25 
10 
.4000 
16 
20 
40 
12 
•3333 
Here for the first time a positive correlation is evident (figs. 3 and 4). 
The most immature leaf in which a differentiation of the bundles has 
occurred^ contains the greatest number of vein-islets per unit area. Further- 
2 Nageli (1855) and Prantl (1883) have shown that the nervature of certain dicoty- 
ledonous leaves is not completely performed in the bud, but that new veins arise as the leaf 
expands. This is the case in leaves of Citrus grandis. The smallest leaves in which the 
bundles would take a differential stain were those measuring not less than 8 millimeters 
(short diameter). 
