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INTRODUCTORY ESSAY. xil 
on this subject upon a very extensive examination of living plants in all latitudes, with my attention 
particularly directed to the influence of external causes, not only on the general phenomena of vegeta- 
tion, but also upon individuals. Added to this, I have paid a great deal of attention to variable 
plants, both of tropical and temperate climates, and studied them in a living state, both wild and cul- 
tivated, and also in the herbarium. The result of my observations is, that differences of habit, co- 
lour, hairiness, and outline of leaves, and minute characters drawn from other organs than those of 
reproduction, are generally fallacious as specific marks, being attributable to external causes, and easily 
obliterated under cultivation. It has hence been my plan to group the individuals of a genus which 
T assume after careful examination to contain many species whose limits I cannot .define, that the 
species shall have the same relative value as those have of allied genera whose specifie characters are 
evident. I doing so I believe I have followed the practice of every systematist of large experience 
and acknowledged judgment since the days of Linnzus, as Bentham, Brown, the De Candolles, 
Decaisne, Asa Gray, Jussieu, Lindley, and the Richards; names which include not only the most 
learned systematists, but the most profound anatomists and physiologists. I am far from supposing 
that the same materials of a difficult group would receive precisely similar treatment at the hands of 
each of these eminent men; but their results would so closely approximate as to be in harmony with 
each other, and available for scientific purposes: with all, the tendency would be to regard dubious 
species as varieties, to take enlarged views of the range and variation of species, and to weigh 
characters not only per se, but with reference to those which prevail in the Order to which the species 
under consideration belong. 
In working up incomplete floras especially, I believe it to be of the utmost importance to adopt 
such a course, and to resist steadily the temptation to multiply names, for it is practically very diffi- 
cult to expunge a species founded on an error of judgment or observation*. There is further an in- 
herent tendency in every one occupied with specialities to exaggerate the value of his materials and 
labours, whence it happens, that botanists engaged exclusively upon local floras are at issue with those 
of more extended experience, the former considering as species what the latter call varieties, and 
what the latter suspect to be an introduced plant the former are prone to consider a native. There is 
much to be said on both sides of such questions: the local botanist looks closer, perceives sooner, 
and often appreciates better, inconspicuous organs and characters, which are overlooked or too 
hastily dismissed by the botanist occupied with those higher branches of the science, which demand 
a wider range of observation and broader views of specialities; and there is no doubt but that the 
truth can only be arrived at through their joint labours; for a good observer is one thing, and the 
knowledge and experience required to make use of facts for purposes of generalization, another : 
minute differences however, when long dwelt upon, become magnified and assume undue value, and 
the gencral botanist must always receive with distrust the conclusions deduced from a few species 
of a large genus, or from a few specimens of a widely distributed plant. 
I have been led to dwell at length upon this point, because I feel sure the New Zealand student 
will at first find it difficult to agree with me in many cases, as for instance on so protean a Fern as 
Lomaria procera, whose varieties (to an inexperienced eye) are more dissimilar than are other species 
of the same genus. In this (and in many similar cases) he must bear in mind that I have examined 
* The state of the British flora proves not only this, but further, that one such error leads to many more of 
the like kind : students are led to over-estimate inconstant characters, to take a narrow view of the importance and 
end of botany, and to throw away time upon profitless discussions about the difference between infinitely variable 
forms of plants, of whose identity really learned botanists have no doubt whatever. 
