re
stimulating by far than that based on scientific classifications, as
orders, families and species. The great and simple outlines of
nature's work begin to appear out of such laws.

Again the study of the whole _life history_ of a plant or animal, in
its relations to the inorganic world and to other plants and animals,
is always a cross-section in the sciences and shows how all the natural
sciences are knit together into a causal unity. 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.

In nature as it shows itself in the woods or in the pond, there is such
a _mingling and interdependence_ of the natural sciences upon each
other that the book of nature seems totally different from books of
botany, physics, and zoology as made by men. In the forest we find
close together trees of many kinds, shrubs, flowering plants, vines,
mosses, and ferns; grasses, beetles, worms, and birds; squirrels, owls
and sunshine; rocks, soil, and springs; summer and winter; storms,
frost, and drouth. Plants depend upon the soil and upon each other.
The birds and squirrels find their home and food among the trees and
plants. The trees seem to grow together as if they needed each other's
companionship. All the plants and animals depend upon the soil, air,
and climate, and the whole wood changes its garb and partly its