nd poplars are very light, and are produced in
immense quantities. Like those of the great willow-herb, they are
beautifully constructed for making long journeys through the air--a
fact that explains the frequency of these trees in burned districts.
A considerable number of seeds and fruits grow with a parachute
attached at one end, not to prevent injury by falling from the tree
top, but to enable the wind to sustain and transport them for a longer
distance.

26. A study of the dandelion.--In spring the dandelion is almost
everywhere to be found; every one knows it--the child to admire, the
gardener to despise. From each cluster of leaves spreading flat in
the grass come forth several hollow stems, short or tall, depending
on the amount of sunshine and shade. Each stem bears, not one flower,
but a hundred or more small ones. Around and beneath each yellow
cluster are two rows of thin, green, smooth scales (involucre).

[Illustration: FIG. 32.--Heads of the dandelion in fruit, closed and
open.]

The short outer row soon curls back, as though for rest or ornament,
or for watching the progress of the colony above; but the inner row
has a very important duty yet to perform in guarding the large family
within. At night, or in daytime, if the day be wet, the long scales
press like a blanket closely about the flowers, and do not permit
them to come out; but when the sun is bright, it shrinks the outer
side of these scales, which then curl apart, leaving the yellow
flowers ready for bees to visit or boys to admire and study. For
several days the flowers of a head blossom in succession, each night
to be snugly wrapped by the scales, and the next day to be again left
open, if the weather be fine. After each flower in turn has been
allowed to see the light, and after all have been crawled over by
bee and wasp to distribute the yellow pollen that seeds may be produced,
there is nothing else to do but patiently wait for a week or two while
receiving food from the mother plant to perfect each little fruit
and seed. During all this period of maturing, day and night, rain
or shine, the scales hold the cluster closely; the stem bends over
to one side, and the rain and dew is kept from entering. After a while,
on some bright morning, the dandelion stalk is seen standing erect
again, and is probably surrounded by many others in a similar position.
The dry air shrinks the outside of the scales, and they turn downward;
the circle of fea