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, witbin 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- 

 ing 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 f. 



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 tbe migrations of man (as Poa 

 annua, Pkalaris Canadensis, 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 scandeut Baulri- , 

 uias), there is nothing in the abnormally developed wood of the climbing BauMnia 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 ease 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 AUinastrum is a conspicuous ex- 

 ample : it is a unisexual water-plant, of which one sex aloue was introduced from North America into England, 

 where it has withiu 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 Jcoms Calamus, a plant spread (not by 

 cultivation) over the whole north temperate hemisphere, which bears hermaphrodite flowers, but very rarely seeds. 



f 1 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 horn 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. 



