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eS 
‘7 
ADDRESS. Ixxix 
Yet I shall not be deemed invidious if I cite one work as eminently exem- 
plary of the spirit and scope of the investigations needed for the elucidation 
of any branch of Natural History. That work is the monograph of the 
Chelonian Reptiles (Tortoises, Terrapenes and Turtles) of the United States 
of America, published last year at Boston, U.S., by Professor Agassiz. 
I cite it, not wholly on account of its intrinsic merits, but also because it 
affords me the opportunity of expressing, on the part of naturalists, the ad- 
miration of, and deep sense of gratitude to, the great and liberal people whose 
perception of the intrinsic value and dignity of pure science has enabled the 
distinguished author to enrich zoology by a work unparalleled in the 
completeness, perfection, and consequent expense of its graphic illustrations. 
“‘ We had fixed,” writes Agassiz, “‘ upon five hundred subscribers as the 
number necessary to enter upon the publication with safety :—at this moment 
it stands at twenty-five hundred,—a support such as was never before offered 
to any scientific man for purely scientific ends, without any reference to 
government objects or direct practical aims*.” 
Geographical Distribution of Plants—Observations of the characters of 
plants, the record of such observations by the Linnzan and subsequently 
improved artifices of description, the application of this power to comparison, 
and deductions from the results of such comparisons,—have led to the 
recognition of the natural groups or families of the vegetable kingdom, and 
to a clear scientific comprehension of that great department of living Nature. 
This phase of botanical science gives the power of further and more pro- 
fitable generalizations, such as those teaching the relations between the par- 
ticular plants and particular localities. 
_ The sum of these relations, forming the Geographical Distribution of 
Plants, rests, perhaps at present necessarily, on an assumption, viz. that each 
species has been created, or come into being, but once in time and space; 
and that its present diffusion is the result of its own law of reproduction, 
under the diffusive or restrictive influence of external circumstances. These 
circumstances are chiefly temperature and moisture, dependent on the distance 
from the source of heat and the obliquity of the sun’s rays, modified by alti- 
tude above the sea-level, or the degree of rarefaction of the atmosphere, and 
of the power of the surface to radiate heat. Both latitude and altitude 
are further modified by currents of air and ocean, which influence 
the distribution of the heat they have absorbed. Thus large tracts of dry 
land produce dry and extreme climates, while large expanses of sea produce 
humid and equable climates. Botany, in short, at this phase becomes inti- 
mately related to climatology; and the traveller, the meteorologist, and the 
naturalist reciprocally aid each other in the acquisition of a knowledge of 
fruitful general laws. Agriculture affects the geographical distribution of 
plants, both direetly and indirectly. It diffuses plants over a wider area of 
_ * Agassiz, “Monograph on North American Testudinata,” 4to, Boston, 1857, Preface, 
P- Vill. vol. i. Of the 2500 Subscribers only 20 are Extra-american. 
