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X FLORA OF NEW ZEALAND.
respiration, and reproduction, ai*e infinitely more Tai’j^blc and susceptible of change and even obliteration
in plants, without affecting the life either of the individual or of the species*. The result o±
these facts is th a t we have the means in animals of appreciating the extent and value of differences,
by combined observations upon structm’e and functions, upon habits and organization, which ive hai^e
not in the vegetable kingdom, and Avhich the phenomena of cultivation assui’e us do not exist to a
degree th a t has, within the limits of our experience, proved available for throwing much light on the
subject.
The ai'guments in favoui* of the permanence of specific characters in plants arc :—
1. The fact th a t the amount of change produced by external causes does not warrant our assuming
the contraiy as a general law. Though there ai'e many notorious cases in which cnlti^■ation
and other causes produce changes of g reater apparent value thau specific characters generally possess,
this happens in comparatively very few families, and only in such as are easily cultivated. In the
whole range of th e vegetable kingdom it is difficult to produce a change of specific value, however
much we may alter conditions; it is much more difficult to prevent an induced variety from reverting
to its original state, though we persevere in supplying the original conditions; and it is most difficult
of all to reproduce a variety with similar materials and processesf-
2. In tracing widely dispersed species, the permanence with which they retain thefr characters
strikes the most ordinaiy observer; and this, whether we take such plants as have been dispersed
without the aid of man (as Sonchus oleraceus, Callitriche, oxidiMontia) through all latitudes from E n g land
to New Zealand; or such as have within modem times followed the migrations of m an (as Poa
annua, Phalaris Canariensis, Dock, Clover, Alsine media, CapseUa bursa-past oris, and a host of o th e rs);
or such as man transports with him, w hether such temperate climate plants as the cerealia, fr’uits, and
flowers of the garden or field, or such tropical forms as Convolvulus Batatas and yams, which were
introduced into New Zealand bv its earhest inhabitants;—all these, in whatever climate to which we
may follow them, retain the impress of their kind, unchanged save in a trifling degree.
Though to a great extent these differences accompany a habit of gi’owth (as in the case of erect and scandent Bauki-
nias), there is nothing in the abnormally developed wood of the chmbing Bauhinia that would lead a skilled physiologist
ignorant of the fact to say that it was better adapted to a climbing than to an erect plant; the function is
experimentally known to be indicated by the structure, but the structure is not seen to be adapted to the functiou.
This is not so in the sister kingdom, for we confidently pronounce an animal to be a climber, because we see that
its organs are adapted to the performance of that function; here the habit is not only indicated by the structure,
but the latter is explained by the function which it enables the animal to fulfil.
* To take an extreme case of this;—many plants are known, in a wild and cultivated state, which propagate
abundantly by roots or division, where they do not do so by seed. Anacharis Ahinasirum is a conspicuous example
: it is a unisexual water-plant, of which one sex alone was introduced from North America into England,
where it has within a few years so spread by division as to be a serious impediment to inland navigation. The
Horse-radish is another example, it being, I believe, never known to seed or even to bear perfect flowers. A still
more remarkable case has been pointed out to me by ifr. Brown, in the Acorus Calamm, a plant spread (not by
cultivation) over the whole north temperate hemisphere, which bears hermaphrodite flowers, but very rarely seeds.
t I am quite aware that this argument will be met by many instances of change produced in our garden
plants; but, after all, the skill of the gardener is successfully exerted in but few cases upon the whole : out of more
than twenty thousand species cultivated at one time or another in the Royal Gardens of Kew, how few there are
which do not come up, not only true to their species, but even to the race or variety from which they spring; yet
it would be difficult to suggest a more complete change than that from the Alps or Polar regions to Surrey, or
from the free air of the tropics to the thoroughly artificial conditions of our hothouses. Plants do not accommodate
themselves to these changes: either they have passive powers of resisting their effects to a greater or less degree, or
they succumb to them.
3. ’With compai’ativcly few exceptions, plants arc confined witlim well-marked limits, which,
though often very wide, are sometimes as much th e reverse ; while the instances are rare of sporadic
species, as suck are called which are found in small numbers in widely sundered localities. These
facts seem incompatible on the one hand w ith the theory of species spreading from many centres, and
on the other with them varjdng indefinitely ; for wore it othermse, sporadic distribution w'ould be the
rule, insular floras would not necessarily be peculiar, and similar climates would have similar, if not
identical species, which is not the case.
4. A midtitnde of allied species of plants grow close together wdthout any interchange of specific
character ; and there are instances of exceedingly closely allied plants keeping company under
many modifications of climate, soil, and elevation, yet never losing the ir distinctive marks.
5. The indiridnals th a t inhabit the circumference of the area occupied by a species, are not
found passing into other species, h u t ceasing more or less abruptly ; the ir limits may meet or overlap
those of one or more very similar species, when the indiriduals associate, h u t do not amalgamate.
6. One negative argument in favour of distribution from one centre only, is, th a t taking the
broadest view of the dispersion of species, we find th a t the more extensive families* are more or less
widely disfributed, very much in proportion to the facilities they present for dispersion. Thus the
most minute-spored Cryptogamsf are the most widely dispersed of all organized n a tu re ; plants th a t
resist the influence of climate best, range farthest ; w^ater-plants are more cosmopolite th an land-
plants, and inhabitants of salt, more than those of fresh water : the more equable and uniform is the
climate of a tract of land, th e more uniformly and widely wiU its plants be distributed.
7. The species of the lowest Orders are not only the most widely diffused, h u t their specific
characters are not modified by the greatest changes of climate, however much their stature and
luxuriance may vary. Fungi offer a remarkable instance of this ; their microscopic spores are wafted
in myriads through the air ; the life of the individuals is often of very short duration, and many of
them being as sensitive as insects to temperature and humidity, they are ephemeral in all senses ;
sometimes appearing only once in the same spot, and remaining h u t a few days, never to reappear
■within the observer's experience. The specific characters of many reside in the diameter, fonn, colour,
and arrangement of tlieir most minute organs, whose analysis demands a refinement of microscopic
skill; yet the most accomplislicd and profound botanist in this N a tu ra l Order (w'ho has favoured me
with the descriptions of the New Zealand Fungi) fails to find the most trifling character by which
to separate many New Zealand species from European.
8. The fact, now universally conceded by all intelligent horticulturists, th a t no plant has been
acclimated in England within the experience of man, is a very suggestive one, though not conclusive;
for it may be answered, th a t plants which cannot survive a sudden change, might a slow and
progi-essive one. On the other hand, plants have pow'crs of enduring change when self-propagated
th a t they have not in our gardens ; thus I find a great difference in the hardiness of individual species
of several Himalayan plants J, depending upon th e altitude at which they were gathered. In these
* This rule does not extend to the Natural Orders themselves. The Composita;, whose facilities for dispersion
arc proverbial, are amongst the most local; and the same may be said oî Leguminosoe and Solaneæ, whose seeds
retain their vitality in a remarkable degree : a few of their species arc remarkably cosmopolite, but the greater number
have generally narrow ranges.
t Tlie fact (first communicated to me by the Rev. M. J. Berkeley) of the spores of Fungi having been found
by Professor Ehrcnberg mingled with the atmospheric dust that has fallen on sldps far out at sea, is one of the
most decisive proofs of this.
X Thus some of the seedling Pines whose parents grew at 12,000 feet appear hardy, whilst tliose of the same
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