DE CANDOLLE ON SPECTES. 
195 
all over Asia Minor, Turkey in Europe, and thence continuously 
westward in the Bannat, Istria, and Lower Austria. Though absent 
in Greece and Zante, it occurs in the Apennines and Sicily, in the 
neighbourhood of Besanqon, and in Western Erance. These isolated 
habitats of the Turkey Oak seem to imply its former continuous ex¬ 
tension from Lebanon to the Atlantic border, and its subsequent local 
extinction, not only by man’s agency, but through physical causes. 
When Oaks occur in isolated patches, due to the extension of the 
species, these patches appear under a different aspect; the localities 
are not so far separated, for acorns are not transported far by 
the wind or by birds; and further, M. De Candolle thinks he has 
demonstrated by his researches in the known naturalization of species 
in Europe and the Colonies, that extension is a rapid phenomenon—■ 
an invasion, in fact—and diminution a slow one. If Q. Cerris, there¬ 
fore, were now invading Europe, it would appear at one time in one 
place and at another time in another, and its inroads would be all the 
more obvious from its fruit being a remarkable object, attracting the 
attention of the most ignorant observer. On the contrary, the above- 
mentioned localities of Q. Cerris are few, and have been the same for 
the last fifty years. 
The above is very ingenious, and perhaps true; but, far from con¬ 
vincing, it assumes too much at every step, and omits all allusion to 
disturbing causes. It assumes, 1. That the progress of migration of 
a tree must be continuous ; from which it follows that all trees whose 
areas of distribution are not continuous are diminishing in those areas. 
2. That birds do not carry seeds so large as acorns, which is open 
to doubt, seeing that Pigeons are granivorous, and moreover have 
been shot in tropical islands with whole nutmegs in their crops. # 
3. That Q. Cerris must once have inhabited Greece. 4. Much 
exception may be taken to the assertion that extension is a rapid 
phenomenon and diminution a slow one, especially when applied to 
trees of long duration. 5. There is no confidence to be placed in 
the powers of observation of uneducated people, and still less in their 
opportunities of observing and in the chances of their observations 
being handed down. 6. The gravest objection of all to the whole 
method of treating the subject is, the involved assumption, that the 
dissemination of a species is an unaided process, depending solely 
on the plant’s fecundity and favouring conditions of climate and 
soil; the struggle for existence is not recognised, the plant is sup¬ 
posed to grow where it likes best, not where alone other plants and 
animals will let it grow; the frail tenure upon which each lives and 
occupies the soil is overlooked, as is the fact that of the thousand 
natural causes which oppose the distribution of a plant, each is the 
* On the authority of Dr. Jenner, in the a Philosophical Transactions,” the 
Woodpigeon has been frequently shot on the Norfolk coast, having in its crop seeds 
of plants that are not cultivated in England. The Crow also is said to be an active 
agent in disseminating Oaks in Wales and Scotland; both the Hooded and Common 
Crow cany the acorns for many miles, and these grow where thus transported. 
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