vitality of a
species," and which excludes "mammalian selection altogether." If this
were true, spines should occur mainly in feeble, rare, and dying-out
species, instead of which we have the hawthorn, one of our most vigorous
shrubs or trees, with abundant vitality and an extensive range over the
whole Palaearctic region, showing that it is really a dominant species.
In North America the numerous thorny species of Crataegus are equally
vigorous, as are the false acacia (Robinia) and the honey-locust
(Gleditschia). Neither have the numerous species of very spiny Acacias
been noticed to be rarer or less vigorous than the unarmed kinds.

On the other point--that spines are not due to mammalian selection--we
are able to adduce what must be considered direct and conclusive
evidence. For if spines, admittedly produced by aborted branches,
petioles, or peduncles, are due solely or mainly to diminished
vegetativeness or ebbing vitality, they ought to occur in all countries
alike, or at all events in all whose similar conditions tend to check
vegetation; whereas, if they are, solely or mainly, developed as a
protection against the attacks of herbivorous mammals, they ought to be
most abundant where these are plentiful, and rare or absent where
indigenous mammalia are wanting. Oceanic islands, as compared with
continents, would thus furnish a crucial test of the two theories; and
Mr. Hemsley of Kew, who has specially studied insular floras, has given
me some valuable information on this point. He says: "There are no spiny
or prickly plants in the indigenous element of the St. Helena flora. The
relatively rich flora of the Sandwich Isles is not absolutely without a
prickly plant, but almost so. All the endemic genera are unarmed, and
the endemic species of almost every other genus. Even such genera as
Zanthoxylon, Acacia, Xylosoma, Lycium, and Solanum, of which there are
many armed species in other countries, are only represented by unarmed
species. The two endemic Rubi have the prickles reduced to the setaceous
condition, and the two palms are unarmed.

"The flora of the Galapagos includes a number of prickly plants, among
them several cacti (these have not been investigated and may be American
species), but I do not think one of the known endemic species of any
family is prickly or spiny.

"Spiny and prickly plants are also rare in New Zealand, but there are
the formidably armed species of wild Spaniard (Aciphylla), one speci