WATER TRANSPORTATION OF PLANTS. 
25 
Fig. 18. — Fruit 
of Asa-Gray 
sedge with an 
inflated sack 
about it. 
like fruit, the shape of the fruit of buckwheat, sinks at 
once when free from everything else, but with 
the dry calyx still attached, it floats with the 
stream. 
15 . An air-tight sack buoys up seeds. — Here 
are several dry fruits of sedges — plants look- 
ing considerably like grasses. There are a 
good many kinds, and most of them grow in 
wet places. The seed-like fruit of those we 
examine are surrounded each by a sack which 
is considerably too large for it, 
as one would he likely to say, 
but in reality it serves to buoy 
the denser portion within, much 
after the plan of the bladder nut. 
In some instances the sack is rather small, 
but a corky growth below the grain helps to 
buoy it on water. 
Sedges that grow on 
dry land usually have 
the sack fitted closely, 
instead of inflated, and the whole 
mass sinks readily in water. Now 
we see the probable reason why the 
sack is inflated in some species of 
sedges and not in others. 
Here are some small, seed-like fruits, achenes, not likely 
to be recognized by every one. They belong to the arrow- 
Fig. 19.— Fruit of 
Carex commu- 
nis , an upland 
sedge, that 
readily sinks 
when placed in 
water; the sack 
fits closely. 
Fig. 20. — Seed-like fruit of 
arrowhead with corky mar- 
gins to float on water. 
