THE AMERICAN BOTANIST. 
51 
center, but they are samaras none the less. Of this latter type, 
with the seed in the center of the wing, we have a most in- 
genious and remarkable example in the twisted samara of the 
Chinese tree-of-heaven (Ailanthus). These samaras are 
borne in great bunches with each samara on its own tiny stalk. 
When they release their hold on the tree, even on a quiet day 
they begin to revolve rapidly upon thir long axis and moving 
hither and yon like a flock of birds in flight dart away to 
pastures new. Even after reaching the earth, a gust of wind 
catching their sails often carries them much farther. 
Possibly just to show her independence of a single method, 
nature has equipped the cluster of basswood seeds with a sail or 
wing made of a leaf. When the blossoms appear, there ap- 
pears with them a narrow green wing or bract, which is fast- 
ened by its midrib to the common flower stalk for about the 
first half of their respective lengths. During the summer 
this broadens and toughens and its tip spreads out at such 
an angle to the flower stalk that when released from the 
tree in autumn a whirling motion is set up that most effect- 
ually retards the descent of the fruit cluster. Without doubt 
this is nature's best parachute. Since the number of fruits 
in the cluster varies, one may wonder whether the angle 
formed by the bract with the fruit stalk is calculated from th^ 
weight of seeds to be carried. One may easily see how very 
much the wing adds to the seed cluster's buoyancy by simul- 
taneously dropping two seed clusters from a height after the 
bract of one has been removed. The bractless one drops like 
a shot; the other very leisurely reaches the earth. The seeds 
of the blue beech or ironwood (Carpinus) are also equipped 
with a bract, but in this case each seed has its own bract, a 
three-lobed object, which helps in dissemination, but which ap- 
pears to be far less effective than the bract of the basswood. 
From the changes which are rung on the modified ovary 
as a source of winged fruits, we may infer that this is nature's 
