June, 1923] SINNOTT AND DURHAM — ANISOPHYLLY IN ACER 
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he concluded that these leaves actually got more light and thus grew larger 
than the upper ones. He also noticed that it was always the leaf on the 
abaxial side of the twig which grew larger, and for this general tendency 
for structures on the outside of lateral shoots to become larger than those 
on the inside, next the mother axis, he proposed the term “exotrophy” 
(1892). He believed this to be due to the better nutrition of these out¬ 
wardly placed structures, and suggested that exotrophy might be an im¬ 
portant factor in anisophylly. Weisse (1895), working with Acer, showed 
by shading experiments that the leaves which were shaded were smaller 
than those in the light. He also put young maples on a horizontal clinostat, 
thus eliminating the effect of gravity, and found that, although anisophylly 
persisted somewhat, it was less marked than in the control plants. Weisse 
stresses gravity rather than light as a factor in anisophylly. He agrees 
with Wiesner that exotrophy is also concerned, but does not believe that 
nutrition is the cause of it. He renamed the phenomenon “ectauxesis,” 
and believed it to be due to inherited morphological factors and perhaps to 
be teleological. Figdor (1897) caused the side shoots of eight species to 
grow vertically; later, he (1904) planted a young maple tree in such a 
position that one of the side branches was vertical, and in this position 
these lateral shoots ultimately lost their anisophylly. Vertical shoots bent 
downward often acquired it. Figdor believes that gravity, light, and 
possibly certain internal factors are at work. Nordhausen (1902) regards 
light as an important factor in leaf asymmetry and anisophylly in Aesculus, 
where those portions of the leaf-blade presumably exposed to greater light 
are thicker than the rest; but holds that light plays but a small part in the 
case of Acer. He regards exotrophy as an important factor. Heinricher 
(1910) concludes that differences in transpiration rate, governed by tempera¬ 
ture, are important in producing anisophylly in Sempervivum. This is 
denied by Doposcheg-Uhlar (1913), who attributes conditions in this genus 
to light and gravity only. Boshart (1911) believes that leaf asymmetry 
(and presumably other phenomena of anisophylly) are controlled chiefly by 
conditions at the growing point, such as the space occupied by the leaf 
primordia and their relation to the rest of the meristem. A survey of the 
literature up to 1909 is presented by Figdor (1909). 
A number of factors may evidently be concerned with the production 
of anisophylly, but there is no unanimity of opinion as to the part played by 
each. The purpose of this paper is to present results of a statistical study 
of leaf measurements on anisophyllous twigs of Acer, the genus which has 
been most frequently studied in this connection, for the purpose of reducing 
the problem to a quantitative basis and in the hope that a knowledge of the 
relative dimensions, shape, and variability of leaves occupying different 
positions on the lateral shoots may produce evidence of value. 
Maple twigs growing horizontally show marked anisophylly. The upper 
member of each vertically oriented pair is distinctly smaller than the lower 
