A QUANTITATIVE STUDY OF ANISOPHYLLY IN ACER 
Edmund W. Sinnott and George B. Durham 
(Received for publication September 23, 1922) 
The fact that lateral or horizontal shoots often differ from vertical 
ones in showing a dorsiventral as opposed to a radial structure has long 
been observed. One aspect of this dorsiventrality in many species is the 
difference in size, and often in shape, between leaves on the upper and those 
on the low'er sides of the branch. To this phenomenon the term “ani¬ 
sophylly” has been applied by Wiesner. The upper leaves are generally 
smaller than the lower ones, and those arising from the sides of the shoot 
are intermediate in size. There has been much discussion as to the factors 
which produce anisophylly—whether gravity, light, or various internal 
conditions are responsible—and the whole problem is of particular interest 
to students of morphogenesis in that it provides a fairly simple case for 
an analysis of some of the factors which determine form. 
Wiesner (1868) and Frank (1868) were the first to consider the problem, 
and both believed anisophylly to be due primarily to gravity. In Picea 
and Acer, Frank twisted horizontal twigs, still attached to the plant, 
through an angle of 180° and tied them there. In Picea, the original 
anisophylly was maintained in the new growth, the leaves now on the upper 
side still being the longer, but the difference was not as marked as before. 
In Acer there was a complete reversal, the originally upper leaves, now 
on the lower side, being much longer than the originally lower ones. He 
found that anisophylly was not as marked in shoots grown in a dark chamber, 
thus suggesting that light might also play a part. Kny (1873) repeated 
Frank’s experiment, using Abies instead, and found that the original 
anisophylly was finally reversed in the second season following the turning 
of the twigs. Frank (1873) also found that in shoots of Thuya there is a 
very definite anatomical difference between the upper and the lower sides. 
This difference was reversed when the twig was twisted through 180°; but 
as a result of shading experiments and on the basis of other evidence, Frank 
concluded that light, rather than gravity or an internal tendency toward 
bilaterality, was the factor involved. Goebel (1880) first suggested that in¬ 
ternal factors were also at work in producing anisophylly. Rosenvinge 
(1889) showed that dorsiventrality may sometimes be due to external and 
sometimes to internal factors. 
Wiesner in his later papers emphasizes more strongly the importance of 
light. At first he regarded the large size and long petioles of leaves on the 
lower sides of anisophyllous shoots as due to etiolation. Later (1894), 
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