84 
PLANTS OF YELLOWSTONE NATIONAL PAKK 
smaller than those of the cranesbills. The 5 parts of the pistil sepa¬ 
rate entirely at maturity forming 5 one-seeded fruits with long 
tails. These fruits are interesting because of the method by which 
they plant themselves. The fruit is covered with stiff hairs which 
point upward, and its lower end is sharp-pointed. The tail, which 
is 1 or 2 inches long, becomes spirally twisted. Whenever it becomes 
moist it untwists, and then when it 
Figure 63.—Prairie flax. Blue. Copy¬ 
right, J. E. Haynes. 
which open in the morning and 
dries it twists again. This twist¬ 
ing and untwisting gradually push 
the pointed fruit into the ground. 
FLAX FAMILY (LXNACEAE) 
A small family but very import¬ 
ant. It furnishes the fibers from 
which linen thread is made, and 
also the seeds from which linseed 
oil is obtained. The family is rep¬ 
resented here only by the Prairie 
flax (Linum lewisii ). This is com¬ 
monly found on dry soil. It oc¬ 
curs at various places in the park, 
including the travertine at Mam¬ 
moth and the geyserite at Old 
Faithful. It is a slender plant, 
usually about a foot high, with 
linear leaves and beautiful blue 
flowers, about an inch in diameter , 
sually close in the afternoon. 
SPUKGE FAMILY (EUPHO&BIACEAE) 
Plants with milky juice and flowers which in some cases are in¬ 
conspicuous and in others very ornamental. In the African desert 
regions, many members of the family resemble American cacti in 
their habits of growth. Euphorbia serpyliifolia is the only member 
of the family that has with certainty been found in the park. It is 
a prostrate, spreading, smooth plant with oblong, toothed leaves 
and inconspicuous flowers. 
Euphorbia albiccmlis has also been reported and may occur here. 
WATEE STAKWOKT FAMILY (CALLITEICACEAE) 
A family of small, slender, water plants with opposite, entire 
leaves and inconspicuous, axillary, imperfect flowers. A staminate 
