ver assert without the
smallest chance of being contradicted by a future fact, that no
carnation or anemone could ever by cultivation be increased to the size
of a large cabbage; and yet there are assignable quantities much
greater than a cabbage. No man can say that he has seen the largest ear
of wheat, or the largest oak that could ever grow; but he might easily,
and with perfect certainty, name a point of magnitude at which they
would not arrive. In all these cases therefore, a careful distinction
should be made, between an unlimited progress, and a progress where the
limit is merely undefined.

It will be said, perhaps, that the reason why plants and animals cannot
increase indefinitely in size is, that they would fall by their own
weight. I answer, how do we know this but from experience?--from
experience of the degree of strength with which these bodies are
formed. I know that a carnation, long before it reached the size of a
cabbage, would not be supported by its stalk, but I only know this from
my experience of the weakness and want of tenacity in the materials of
a carnation stalk. There are many substances in nature of the same size
that would support as large a head as a cabbage.

The reasons of the mortality of plants are at present perfectly unknown
to us. No man can say why such a plant is annual, another biennial, and
another endures for ages. The whole affair in all these cases, in
plants, animals, and in the human race, is an affair of experience, and
I only conclude that man is mortal because the invariable experience of
all ages has proved the mortality of those materials of which his
visible body is made:

What can we reason, but from what we know?

Sound philosophy will not authorize me to alter this opinion of the
mortality of man on earth, till it can be clearly proved that the human
race has made, and is making, a decided progress towards an illimitable
extent of life. And the chief reason why I adduced the two particular
instances from animals and plants was to expose and illustrate, if I
could, the fallacy of that argument which infers an unlimited progress,
merely because some partial improvement has taken place, and that the
limit of this improvement cannot be precisely ascertained.

The capacity of improvement in plants and animals, to a certain degree,
no person can possibly doubt. A clear and decided progress has already
been made, and yet, I think, it appears that it would be highly