June, 1923] SINNOTT AND DURHAM — ANISOPHYLLY IN ACER 283 
Differences in Shape 
The leaf groups also differ in shape. It will be noted that the members 
of the vertical pairs are symmetrical, the right and left main veins being 
equal. In the horizontal leaves, however, the lower or abaxial main lateral 
veins (right vein of the right leaf and left vein of the left) are distinctly 
longer than the upper ones, this difference being more than five times its 
probable error. 
In the ratio of petiole length to blade (midrib) length the four groups 
also differ, as is shown in table 2. In the vertical lower leaves the petiole 
is far longer in proportion to the blade than it is in the vertical upper; and 
the members of the horizontal pairs are again intermediate. 
Table 2. Ratio of Blade Length to Petiole Length in the Four L,eaf Groups 
Blade Length 
Petiole Length 
Vertical upper. 1.69 
Vertical lower.95 
Horizontal right. 1.11 
Horizontal left. 1.11 
Finally, the four groups differ in blade shape, as shown by the width-to- 
length ratio in table 3. The vertical upper leaves are relatively short and 
broad, the vertical lower ones relatively long and narrow, and the hori¬ 
zontals intermediate. 
Table 3. Ratio of Blade Width to Blade Length in the Four Leaf Groups 
Blade Width 
Blade Length 
Vertical upper. 145 
Vertical lower. 1.29 
Horizontal right. 1.35 
Horizontal left. 1.33 
Differences in Variability 
A study of table 1 shows that some dimensions are much more variable 
than others, 1 petiole length having the highest coefficient of variability and 
blade thickness the lowest. For any given size character the four groups 
also differ in variability in many cases. In every instance (except blade 
thickness), the vertical upper leaves are much more variable than the 
horizontal ones, and the vertical lower are usually intermediate. Although 
the difference between the vertical upper and the horizontal leaves is not in 
every case significant in comparison with its probable error, the figures 
justify us in regarding the vertical upper leaves as the most variable of the 
four groups. 
1 The coefficients of variability for those size characters which involve two dimensions 
(blade area) or three dimensions (blade volume) are of course necessarily higher than, and 
thus not comparable with, those involving only one dimension. 
