DE CANDOLLE ON SPECIES. 
201 
ab initio produxit infinitum Ens ; quse formse, secundum generations 
inditas leges, produxere plures, at sibi semper similes. Ergo species 
tot sunt, quot diversse formse s. structure hodienutn occurrunt,”— 
and the same facts are stated in much the same words in the Ratio 
Operis of his Genera Plantarum. 
It is difficult to drawfrom M. De Candolle’s Essay any positive con¬ 
clusion as to whether or not he has become a convert to Mr. Darwin’s 
theories of evolution and natural selection; though his sixth conclu¬ 
sion binds him to the acceptance of the doctrine of evolution, as far as 
any naturalist, even Mr. Darwin himself, can feel bound by a theory 
built on circumstantial evidence, which from its very nature never 
can be proved: —to the subject of natural selection he does not 
allude in his concluding remarks :•—with regard to the slowness of 
the operation of an assumed creation by evolution, upon which he 
dwells, this is a point upon which Darwin insists as strongly as any 
one; and lastly, with regard to the absence of direct proof, which 
M. De Candolle puts forward as a desideratum, he elsewhere avows 
that the alternative doctrine of original creations is incapable of 
direct proof; so that putting all three considerations together, he 
seems logically driven to the acceptance of evolution as the only 
hypothesis which in the present state of science is tenable. How¬ 
ever this may be, it cannot but be gratifying to British naturalists 
to recognise the enormous change of opinion, and, as we really think, 
advance in philosophical views and range, which this essay manifests 
when contrasted with the otherwise admirable Geographie Botanique 
of the same author, published only eight years ago, and to attribute it, 
as they must, to the influence of the writings of the exclusively Eng¬ 
lish school, founded by Lyell, Darwin, and E. Eorbes. 
XY.— On Welwitschia, a new genijs oe Gnetaceae. By 
Joseph Dalton Hooker, M.D., E.R.S., &c. (Transactions of the 
Linnean Society, xxiv. 1.) 
Our botanical readers must well recollect the lively curiosity excited 
on the publication of Dr. Welwitsch’s letter to Sir William 
Hooker, dated from Loanda, August, 1860, in which he first told us 
of the very extraordinary production with which his name is now 
associated by Dr. Hooker. Yery various were the guesses hazarded 
as to its probable affinities. Guesses they could only be from the 
brief and insufficient account which Dr. Welwitsch was at that time 
in a position to give of his wonderful discovery. It might be some 
uncouth monocotyledon ; in its hexandrous ‘ bi-sexual’ flowers allied 
to the Lilies, or, in its amentiform inflorescence to the Sedges. But 
the vegetative system of the plant offered then the most profound 
enigma. Dr. Welwitsch described it as with an obconic woody 
trunk, having a disc-like top, 1—5 ft. in diameter, from the opposite 
