squirrel will gather acorns where he can possibly get hickory nuts, and
few will gather hickory nuts where the larger and thinner-shelled walnuts
are to be had for the picking. The squirrel is provident, but no more so
than he is fastidious in the choice of his food. He never plants acorns
except for his own gratification, and is never gratified with indifferent
food so long as he can command that which is to his liking.

In further speaking of the "exhausted elements" of the soil--those
necessary for the food of trees as well as plants, and without which they
inevitably perish and disappear--Mr. Emerson says; "This is clearly
indicated in what is constantly going on in the forests, particularly the
fact which I have already stated, and which is abundantly confirmed by my
correspondents, that a forest of one kind is frequently succeeded _by a
spontaneous growth of trees of another kind._" In the sense in which he
manifestly uses the term "spontaneous" in this connection, his new forest
might be accounted for on the theory of "primordial germs," but not on
that of "seeds;" for few trees or shrubs in Massachusetts bear winged
seeds, or possess any other means of dispersion (the _Acer_ family
excepted) than those common to our general forest growths. Spontaneity, in
a strictly scientific sense, is not predicable upon the artificial or
chance sowing of either acorns, hickory nuts, or the chits to pine cones.
A spontaneous growth implies a process which is neither usual nor
accidental--a growth without external cause, but from inherent natural
tendency--and it is questionable whether there is any such process in
nature. It belongs to the same class of idle speculations as "spontaneous
generation" in the infusorial world--a subject that will be considered as
we advance in this work.

Our vegetable physiologists, Mr. Emerson among the number, are simply
unfortunate in their use of terms--those expressing even the commonest