SELF-FERTILIZATION OF PLANTS. 391 
It is immaterial to consider how they got into far distant countries; for it is not the 
method of transportation, but the reason for their establishment that I am considering. 
Many weeds invariably accompany Europeans on migration; but many others are found 
located in places which do not warrant the idea that man has either intentionally or 
unintentionally imported them; and they must now be regarded as natives. Several 
are water-plants, which may be regarded as perhaps the easiest to transport, as aquatic 
birds will readily disperse them; but the question at issue is, although they may be 
transported with ease, why do they maintain their ground when in competition with the 
native indigenous plants? The question is equally pertinent for aquatic as well as 
terrestrial plants, as competition occurs in both cases. The reply I would give is, that 
it is the self- or wind-fertilizing plants which alone can maintain their ground, because 
they are independent of insects, and that having been once introduced into new climatic 
conditions they acquire new and often great constitutional vigour, and so beat their 
native rivals, who, having long since arrived at a standard of equilibrium, cannot acquire 
any new vigour at all proportionate to that infused into the new comers, which thus 
overcome them in every way. 
17. The world-wide distribution of self-fertilizing British plants. 
In the following enumeration I will limit myself, for brevity sake, to such species only 
as are recorded as growing in at least four distinct localities, i. e. as far as my researches 
into “ floras” have enabled me to discover. Many other species are in one, two, or even 
three countries; but the point I particularly wish to bring out is, that whenever British 
plants are found very widely dispersed they are probably almost always self-fertilizing 
or else anemophilous plants. How they have become located where they now are is a 
question with which I am not now concerned; but I only wish to show that such plants, 
having somehow reached far distant localities, have succeeded in establishing themselves ; 
and the method of doing so is, I believe, mainly because they were self-fertilizing and 
consequently independent of insects *. | 
RANUNCULACEX. Ranunculus hydrocharis: forms of this species are recorded from 
S. Austr., Tas., S. Af., S. Am., N.E. Af, N.E. Asia, Cal. R. sceleratus T, Trop. As., 
S. Af., Hong., Jap., N.E. Asia. 
Crucirerm. Brassica oleracea, Jap., Mad., N.Z.; B. rapa, Trop. As., Jap., N. Z., 
And. | 
Cardamine hirsuta, Chili, S. Austr., A. & C., N. Z., F. & F., Tas, 8. Af, Trop. 
Asia, N.E. Af., Hong., Mad., N.E. Asia, Kam. [For the sake of comparison, I will add 
C. pratensis (doubtfully according to Hooker), Tas.; C. impatiens, Temp. Asia and Jap.) 
* In the list which follows I have used the following abbreviations:—S, Austr. (South Australia); Tas. (Tasmania); 
S. Af. (South Africa); S. Am. (South America); N.E. Af. (i. e. North-east Africa); Trop. As. (Tropical Asia, south 
of Himalayas); A. & C. (Auckland and Campbell's Islands) ; N. Z. (New Zealand); F. & F. (Falkland and Fuegia); 
Hong. (Hongkong); Mad. (Madeira); And. (Andaman Isles); Jap. (Japan); Kerg. (Kerguelen Isle); Soe. I. (So- 
ciety Isles); Norf. I. (Norfolk Isle); Cal. (California); Kam. (Kamtschatka). 
_ t Many of the forms of our British species found in foreign countries are not identically the same as ours, but 
varieties of them. This is no more than might be expected (antea, p. 389); still it does not affect the question of p 
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