284 A TEXTBOOK OF GENERAL BOTANY 

Fig. 277. Fruit of linden, 
adapted to wind dispersal 
by being attached to a 
specialized leaf (bract). 
(x3) 
may be both flattened and winged (Fig. 
274). This type of structure results 
in the scattering of the seed by the 
wind. 
Feathery appendages. Seeds (Fig. 
259) or fruits (Fig. 278) may have 
feathery appendages which greatly in- 
crease their buoyancy, so that they are 
frequently carried by the wind to con- 
siderable altitudes. These feathery 
appendages are very characteristic of 
the seeds of milkweeds (Fig. 259) and 
of the achenes of many composites 
(Fig. 278). Commercial cotton. con- 
sists of trichomes which grow from 
the epidermal cells of the seed of the 
cotton plant. These trichomes form a 
flossy mass around the seed. 
Censer mechanisms. The capsules 
of many plants open in such a way 
that the seeds can escape only when 
the capsules are violently shaken, as by a strong wind (Figs. 257, 
279, 280). This has a tendency to scatter the seeds. The seeds 
may in addition have a flat 
shape (Fig. 279) or winged 
outgrowths ; and as they are 
most likely to escape when 
there is a strong wind, they 
may be blown for consider- 
able distances. 
Dispersal by water. Adap- 
tations for dispersal by water 
are not sO common as are 
those for dispersal by wind, 
but the former occur in 
many seashore and aquatic 

Fie. 278. Fruits (achenes) of iron- 
weed (Vernonia), suited to dispersal 
by wind on account of their hairy 
appendages 
