ECOLOGY OF FRUITS - 195 
240. Study of Transportation by Water. — Nothing less 
than a long series of observations by the pond-margin and. 
the brookside will suffice to show how general and impor- 
tant is the work done by water in carrying the seeds of 
aquatics. An experiment will, however, throw some light 
on the subject. 
EXPERIMENT XX 
Adaptation for Transportation by Water.— Collect fruits of as 
many aquatic, semi-aquatic, or riverside and brookside species of 
plants as possible, place them on shallow pans of water, and notice 
what proportion of all the kinds studied will float. Leave them 
twenty-four hours or more and see whether all the kinds that floated 
at first are still afloat. Some desirable fruits for this experiment 
are aquatic grasses, rushes and sedges, polygonums, water-dock, 
bur-reed, arrowhead, water-plantain, pickerel-weed, alder, button- 
bush, water-parsnip (Sium), water-hemlock (Cicuta), water penny- 
wort (Hydrocotyle), lotus (Nelumbo). 
241. Distances traversed by Floating Seeds. — Ocean 
currents furnish transportation for the longest journeys 
that are made by floating seeds. It is a well-known fact 
that cocoa-palms are among the first plants to spring up 
on newly formed coral islands. The nuts from which 
these palms grew may readily have floated a thousand 
miles or more without injury. On examining a cocoanut 
with a fibrous husk attached, just as it fell from the tree, 
it is easy to see how well this fruit is adapted for trans- 
portation by water. There are altogether about a hundred 
drifting fruits known, one (the Maldive nut) reaching a 
weight of from twenty to twenty-five pounds. 
242. Burs. — A large class of fruits is characterized by 
the presence of hooks on the outer surface. These are 
