1883.] Means of Plant Dispersion. 813 
In contrivances for scattering fruits or seeds by wind agency, it 
is plain that their mass must be relatively small and light, or if 
large or heavy the buoyant part must predominate. The prob- 
lem is to overcome the lightness of the air by a substance specifi- 
cally heavier, which may, however, by the aid of currents of air 
acting on some equipment, be wafted away from the parent stock. 
The germ of a new plant may in this way be taken up and carried 
a few feet or yards, or even many miles.. The modifications of 
fruit to secure this end will be noticed first, some of the most 
common examples being taken for illustration. 
The samara, or key-fruit of the maple, is a familiar case. When 
the key is double, as in the common maples and Negundo, each 
part has a striking resemblance to the wing of an insect, being 
thicker and narrower at the base, thinner and broader at the top. 
In the ash the wing has a spatulate form; in the elm and birch 
it is oval, the wing encircling the fruit. In the hop tree (Ptelea 
trifoliata) it is similar, being almost circular. A contrivance much 
like a samara is found in Liriodendron, the tulip tree. The nu- 
merous pistils of a single flower are attached to a common axis, 
making a cone-shaped collection as a whole. Each carpel is fur- 
nished with a wing, pointing upward along the axis, and as they 
fall away separately they may be taken and borne off by the wind. 
If the fall of the samara, or key-fruit of the maple or ash be 
watched, the usefulness of this appendage is easily discerned. It 
falls with a whirling motion, like a stone with a shingle tied to it, 
and may be carried to quite a distance even by a slight breeze, 
and much farther if the wind be high. 
Smaller but similar growths from the fruit are found in some of 
the Umbelliferz, as in the carrot, parsnip, cow parsnip (Heracleum 
lanatum), Polytenia, Archemora and Archangelica. In these the 
achenia are more or less winged, as may be seen in the so-called 
seeds of the carrot and parsnip of the shops. 
Here also must be placed that adaptation for dispersion seen in 
the common basswood (Tilia), a bract growing from the peduncle. 
In form like the wing of a samara, it serves to carry the nuts 
attached to the lower end of the stem and its branches, away from 
the parent tree, and its gyrations while doing so are rather pecu- 
liar and complicated. In the hop hornbeam (Osirya virginica) 
and the blue beech (Carpinus americanus), the enlarged bracts of 
the involucre, becoming dry when the fruit ripens, serve to bear 
