280 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
and differs from it somewhat in shape. The members of the horizontally 
oriented pair are intermediate in most characters between the upper and 
the lower members of the vertical pair. They are also asymmetrical, the 
lower one of the two main lateral veins being longer than the upper. 
iooo leaves of Acer sacchamm, growing on twigs which were horizontal 
or essentially so, were studied. In order to avoid possible genetic differ¬ 
ences, they were all taken from a single tree of this species. Only those 
twigs were chosen in which the successive leaf pairs were clearly vertical 
and horizontal, all those in which the pairs were at all oblique in their 
insertion being eliminated. Twigs were chosen from all parts of the crown 
of the tree. All the leaves on each twig were recorded, so that there is an 
equal representation of those from the basal, median, and terminal regions 
of the year’s growth. Leaves were harvested in midsummer after complete 
maturity had been reached. Length of petiole, length of midrib, width of 
blade from tip to tip of the lateral lobes, and length of right and left main 
vu 
VL 
Fig. i. Diagram representing the four groups of leaves, dimensions proportional to 
the means in table i. VU, vertical upper leaf; VL, vertical lower; HR, horizontal light; 
HL, horizontal left. 
