x FLORA OF NEW ZEALAND. 
respiration, and reproduction, are infinitely more variable and susceptible of change and even oblite- 
ration in plants, without affecting the life either of the individual or of the species*. The result of 
these facts is that we have the means in animals of appreciating the extent and value of differences, 
by combined observations upon structure and functions, upon habits and organization, which we have 
not in the vegetable kingdom, and which the phenomena of cultivation assure us do not exist to a 
degree that has, within the limits of our experience, proved available for throwing much light on the 
subject. 
The arguments in favour of the permanence of specific characters in plants are :— 
1. The fact that the amount of change produced by external causes does not warrant our assum- 
jng the contrary as a general law. Though there are many notorious cases in which cultivation 
and other causes produce changes of greater apparent value than specific characters generally possess, 
this happens in comparatively very few families, and only in such as are easily cultivated. In the 
whole range of the 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 processes T. 
2. In tracing widely dispersed species, the permanence with which they retain their characters 
strikes the most ordinary observer; and this, whether we take such plants as have been dispersed 
without the aid of man (as Sonchus oleraceus, Callitriche, and Montia) through all latitudes from Eng- 
land to New Zealand; or such as have within modern times followed the migrations of man (as Poa 
annua, Phalaris Canariensis, Dock, Clover, Alsine media, Capsella bursa-pastoris, and a host of others) ; 
or such as man transports with him, whether such temperate climate plants as the cerealia, fruits, and 
flowers of the garden or field, or such tropical forms as Convolvulus Batatas and yams, which were 
introduced into New Zealand by its earliest 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 growth (as in the case of erect and scandent Bauhi- 
nias), there is nothing in the abnormally developed wood of the climbing Bauhinia that would lead a skilled physio- 
logist 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 function. 
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 Alsinastrum is a conspicuous ex- 
ample: 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 Mr. Brown, in the 4corus Calamus, a plant spread (not by 
cultivation) over the whole north temperate hemisphere, which hears hermaphrodite flowers, but very rarely seeds. 
+ Lam 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 
[o] 
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. 
