the ground beyond them already
occupied by other plants, who will not tolerate a fresh mouth,
having only just enough to feed themselves. Take the case of
Saxifraga hypnoides and S. umbrosa, "London pride." They are two
especially strong species. They show that, S. hypnoides especially,
by their power of sporting, of diverging into varieties; they show
it equally by their power of thriving anywhere, if they can only get
there. They will grow both in my sandy garden, under a rainfall of
only 23 inches, more luxuriantly than in their native mountains
under a rainfall of 50 or 60 inches. Then how is it that S.
hypnoides cannot get down off the mountains; and that S. umbrosa,
though in Kerry it has got off the mountains and down to the sea-
level, exterminating, I suspect, many species in its progress, yet
cannot get across County Cork? The only answer is, I believe, that
both species are continually trying to go ahead; but that the other
plants already in front of them are too strong for them, and
massacre their infants as soon as born.

And this brings us to another curious question: the sudden and
abundant appearance of plants, like the foxglove and Epilobium
angustifolium, in spots where they have never been seen before. Are
there seeds, as some think, dormant in the ground; or are the seeds
which have germinated, fresh ones wafted thither by wind or
otherwise, and only able to germinate in that one spot because there
the soil is clear? General Monro, now famous for his unequalled
memoir on the bamboos, holds to the latter theory. He pointed out
to me that the Epilobium seeds, being feathered could travel with
the wind; that the plant always made its appearance first on new
banks, landslips, clearings, where it had nothing to compete
against; and that the foxglove did the same. True, and most
painfully true, in the case of thistles and groundsels: but
foxglove seeds, though minute, would hardly be carried by the wind
any more than those of the white clover, which comes up so
abundantly in drained fens. Adhuc sub judice lis est, and I wish
some young naturalists would work carefully at the solution; by
experiment, which is the most sure way to find out anything.

But in researches in this direction they will find puzzles enough.
I will give them one which I shall be most thankful to hear they
have solved within the next seven years--How is it that we find
certain plants, namely, the thrift and the scurvy