BRIEFER ARTICLES. 
_ VARIATION IN LEAF ARRANGEMENT IN A MAPLE. 
Some weeks ago my attention was called by a colleague here to a 
young maple tree growing against the south wall of one of the college 
buildings. This young tree, perhaps ten years old, is limited in its direc- 
tion of growth by its position, and it receives direct sunlight only when 
the sun is sufficiently high to shine over the flight of stone steps just 
east of it. Thus it has only a partial eastern exposure, no northern 
exposure, and is free only at the south and west. Naturally the tree is 
unsymmetrical and leans southward, away from the building. Evidently, 
too, the tree has undergone hardship other than that of unfavorable, 
or at least limited position, for it has no main stem, and its two or three 
largest branches do not balance well. 
Of these larger branches one is remarkable in the arrangement of 
leaves and branchlets. The leaf arrangement of this tree is normally 
opposite, the pairs of leaves alternating regularly, and bearing 4 bud 
in each axil. The buds of former years have developed normally, in 
pairs and alternating. One branch, however, pointing southward an 
upward atan angle of about 45°, bears leaves and branchlets !n 
threes, the whorls of three alternating regularly, so that the leaves and 
branches do not stand directly over one another. The branchlets, on 
the contrary, bear leaves in pairs, regularly alternating and therefore 
typical in arrangement. 
On examining the lateral buds which are borne in the axils of the 
leaves developed in whorls of three, one sees a possible reason for such 
a diversity in the phyllotaxy of the branch and of its branchlets. 
Obviously each axillary bud develops in a space limited by two opposite 
organs, branch and leaf, capable of offering a certain amount of resist- 
ance to any structure developing between them. But on the other two 
sides no such resistance can be offered, for there is no older and stronger 
structure. It is true that the base of the petiole of the maple leaf Is 
concave on the upper side, and that it clasps the branch more 
or less; but obviously far more resistance can be offered to cea 
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