FIELDBOOK OF ILLINOIS WILD FLOWERS 
fruit in question: though these differences seem trivial at times, 
they are very important in referring the plant in question to its 
appropriate family in its classification. They tell us whether 
the fruit is the product of a flower cluster or a single flower, 
whether it came from the ovary of a flower which was free from 
the calyx or one which was united with the calyx, etc. 
DISSEMINATION 
Some fruits are disseminated while still containing their 
seeds, which are shed from them later; other fruits shed their 
seeds while still attached to the plant. 
Seed dispersal structures and agents of dissemination.—The 
fruit of the elm and ash illustrate the samara, or “‘key fruit,” 
which has wings that readily provide dispersal by wind. Fruits 
of the maple and box-elder are often double. 
Many seeds of the dehiscent fruits are provided with special 
parts which facilitate their dissemination. The seeds of milk- 
weeds and cottonwood have tufts of long hairs, outgrowths 
of the seed coats. Seeds of the catalpa tree are flat and fringed 
on the margins so they are easily borne by the wind. Such 
naked seeds outwardly resemble but are not true samaras, in 
that true samaras are fruits containing seeds. When the fruits 
of the touch-me-not, violets, the lupine and wild geranium split 
open, the seeds are thrown out with such violence that they are 
propelled through a considerable distance. Thus the variety 
of methods by which fruits and seeds are disseminated is so 
great that close observers may still hope to discover some special 
method which has not been fully described in a textbook, and 
many nature lovers derive great pleasure and satisfaction from 
the pursuit of their observations on seed dissemination. Some 
naturalists make extensive collections illustrating the great 
variety of methods of seed dispersal. 
Water is less common than wind as an agent of dissemination, 
but is important in that it may carry fruits or seeds for long 
distances. Many seeds and fruits are lighter than water and 
will float almost indefinitely, as, for example, seeds of the larger 
blue flag; they are protected by a corky outer layer that water- 
proofs them for a considerable time. Such seeds, however, at 
length absorb water and sink, or continue to float but lose their 
ability to germinate. Consequently, there is a limit to the dis- 
tance and time they may be transported by water and still 
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