118 
PLANTS OF YELLOWSTONE NATIONAL PAEK 
but at the same time one of the most successful. More than one-fifth 
of the plants described in this book belong to this family. Very 
many of the members of the composite family are used as ornamental 
plants and still larger numbers are prized as wild flowers. The fam¬ 
ily also contains many pernicious weeds, but relatively few plants 
that are used as food by man. Lettuce is undoubtedly the most 
widely used food plant belonging to this family. The great major¬ 
ity of the members of the family are herbs, although there are also 
many shrubs, and the success of the family in spreading to all parts 
of the earth is due largely to the remarkable adaptations for seed 
dissemination, mostly by wind or animals, possessed by many of its 
members. 
The chief characteristic of the family that distinguishes it from 
all others is that the relatively small flowers are borne in a dense 
head, all on one receptacle, and are surrounded by an involucre of 
bracts. What we commonly call a flower of a dandelion, sunflower, 
aster, or chrysanthemum is not a single flower but a whole bouquet 
of flowers. Each of the little, yellow, petallike parts of a dandelion, 
for example, is an individual flower. In such a flower the ovary is 
inferior, that is, the other parts of the flower are attached above 
the ovary. At the top of the ovary is a cluster of white hairs called 
the pappus, which represents the calyx. In some members of the 
family the pappus consists of bristles, awns, scales, or teeth, and in 
some cases it is lacking entirely. Within and above the pappus 
the yellow, strap-shaped part of the dandelion flower which is tne 
corolla and is made up of five very narrow petals united together. 
In the center of the flower is a single style with two stigmas at the 
end, and around this are the five stamens with the filaments distinct, 
but the anthers united around the style. Most of the parts of such 
a flower are shown in plate VI. 
The advantage of having a large number of flowers together on 
one receptacle is obvious. They can be small and still conspicuous 
enough to attract insects, and once an insect has been attracted it is 
likely to visit a number of flowers before leaving. In the aster and 
many other members of the family there are two kinds of flowers 
in each head. The outer ones are similar to those of the dandelion 
and are called ray flowers, while the inner ones have tubular corol¬ 
las and are called disk flowers. Often the ray flowers differ in color 
from the disk flowers, and in some cases the ray flowers do not pro¬ 
duce any fruits, their purpose being to attract insects, while the less 
conspicuous disk flowers produce the fruits. The insects, of course, 
visit the flowers for food, that is, for the nectar which they either 
use directly for food or from which they may make honey, and while 
obtaining this food they accidentally bring about a transfer of pollen 
from anthers to stigmas. 
