ond kind was rare at first, but afterwards
became more frequent. A third, the Egyptian wheat (_T. turgidum_), does not
agree exactly with any existing variety, and was rare during the Stone
period. A fourth kind (_T. dicoccum_) differs from all known varieties of
this form. A fifth kind (_T. monococcum_) is known to have existed during
the Stone period only by the presence of a single ear. A sixth kind, the
common _T. spelta_, was not introduced into Switzerland until the Bronze
age. Of barley, besides the short-eared and small-grained kind, two others
were cultivated, one of which was very scarce, and resembled our present
common _H. distichum_. During the Bronze age rye and oats were introduced;
the oat-grains being somewhat smaller than those produced by our existing
varieties. The poppy was largely cultivated during the Stone period,
probably for its oil; but the variety which then existed is not now known.
A peculiar pea with small seeds lasted from the Stone to the Bronze age,
and then became extinct; whilst a peculiar bean, likewise having small
seeds, came in at the Bronze period and lasted to the time of the Romans.
These details sound like the description given by a palaeontologist of the
mutations in form, of the first appearance, the increasing rarity, and
final extinction of fossil species, embedded in the successive stages of a
geological formation.

{320}

Finally, every one must judge for himself whether it is more probable that
the several forms of wheat, barley, rye, and oats are descended from
between ten and fifteen species, most of which are now either unknown or
extinct, or whether they are descended from between four and eight species,
which may have either closely resembled our present cultivated forms, or
have been so widely different as to escape identification. In this latter
case, we must conclude that man cultivated the cereals at an enormously
remote period, and that he formerly practised some degree of selection,
which in itself is not improbable. We may, perhaps, further believe that,
when wheat was first cultivated, the ears and grains increased quickly in
size, in the same manner as the roots of the wild carrot and parsnip are
known to increase quickly in bulk under cultivation.

_Maize: Zea Mays._--Botanists are nearly unanimous that all the
cultivated kinds belong to the same species. It is undoubtedly[565] of
American origin, and was grown by the aborigines throughout th