ley had
been cultivated, we should of course be compelled to look at these forms as
distinct species. But, as Heer has remarked, agriculture even at the period
of the lake-habitations had already made considerable progress; for,
besides the ten cereals, peas, poppies, flax, and apparently apples, were
cultivated. It may also be inferred, from one variety of wheat being the
so-called Egyptian, and from what is known of the native country of the
panicum and setaria, as well as from the nature of the weeds which then
grew mingled with the crops, that the lake-inhabitants either still kept up
commercial intercourse with some southern people or had originally
proceeded as colonists from the South.

Loiseleur-Deslongchamps[560] has argued that, if our cereal plants had been
greatly modified by cultivation, the weeds which habitually grow mingled
with them would have been equally modified. But this argument shows how
completely the principle of selection has been overlooked. That such weeds
have not varied, or at least do not vary now in any extreme degree, is the
opinion of Mr. H. C. Watson and Professor Asa Gray, as they inform me; but
who will pretend to say that they do not vary as much as the individual
plants of the same sub-variety of wheat? We have already seen that pure
varieties of wheat, cultivated in the same field, offer many slight
variations, which can be selected and separately propagated; and that
occasionally more strongly pronounced variations appear, which, as Mr.
Sheriff has proved, are well worthy of extensive cultivation. Not until
equal attention be paid to the variability and selection of weeds, can the
argument from their constancy under unintentional culture be of any value.
In accordance with the principles of selection we can understand how it is
that in the several cultivated varieties of wheat the organs of vegetation
differ so little; for if a plant {318} with peculiar leaves appeared, it
would be neglected unless the grains of corn were at the same time superior
in quality or size. The selection of seed-corn was strongly
recommended[561] in ancient times by Columella and Celsus; and as Virgil
says,--

"I've seen the largest seeds, tho' view'd with care,
Degenerate, unless th' industrious hand
Did yearly cull the largest."

But whether in ancient times selection was methodically pursued we may well
doubt, when we hear how laborious the work was found by Le Couteur.
Although the principle