Take the life history
of a _hickory tree_. As it germinates and grows from the seed how it
draws from the earth and air; the effect of storms, seasons, and
lightning upon it; how it later furnishes nuts to the squirrels and
boys; its branches may be the nesting place for birds and its bark for
insects. Finally, the uses of its tough wood for man are seen. The
life of a squirrel or of a honey-bee furnishes also a cross-section
through all the sciences from the inorganic world up to man.
If in tracing life histories we take care to select _typical_ subjects
which exemplify perhaps thousands of similar cases, we shall materially
shorten the road leading toward insight into nature. These types are
concrete and have all the interest and attractiveness of individual
life, but they also bring out characteristics which explain myriads of
similar phenomena. A careful and detailed study of a single tree like
the maple, with the circulation of the sap and the function of roots,
bark, leaves, and woody fiber, will give an insight into the processes
of growth upon which the life of the tree depends and these processes
will easily appear to be true of all tree and plant forms.
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