926 
ORIGIN OF SPECIES, 
six to twenty in number; they may be white, yellow, red, orange, violet, streaked 
with black, blue, or copper- red; their weight varies sevenfold; their form also varies 
extremely; there are varieties with three kinds of fruit of different form and colour 
on one rachis ; and a great number of other differences also occur ^ These 
instances may suffice to show to what an extent the amount of deviation of the 
varieties of a primitive form may increase under cultivation ^. 
It is much more difficult, and to a great extent impossible, to prove directly to 
what extent the variation of wild forms can increase without cultivation, because 
historical evidence is in this case generally impossible, or can only be obtained indi- 
rectly or conjecturally. But since the laws of variation are unquestionably the same 
in the case of wild as of cultivated plants — although they operate in the two cases 
under different conditions — we may for the present at least assume as probable that 
plants vary as greatly in the wild as in the cultivated state. We shall however in the 
sequel have to examine a number of weighty considerations which lead to the con- 
clusion that variation has produced infinitely greater effects in originating the various 
wild forms of plants than those which we perceive in cultivated varieties ^. 
The variation of cultivated plants shows that there is only one cause for the 
internal and for the external hereditary resemblance between different plants, and 
that this cause is the common origin of similar forms from one and the same 
ancestral form. When we meet with corresponding phenomena in wild forms, and 
when we find that with them dissimilar forms are connected by a series of inter- 
mediate forms, just as we find to be the case between the primitive forms of culti- 
vated plants and their most abnormal varieties, we are forced to the conclusion that 
in wild plants also a similar affinity is the only cause of resemblance. The extra- 
ordinarily numerous forms, for example, of the widely distributed genus Hieracium 
present phenomena similar in many respects to those of cultivated Gourds, Cab- 
bages, &c. In addition to a number of forms which are considered to be species, 
there are a still greater number of intermediate forms, some of which only are 
hybrids, the greater part perfectly fertile varieties. Nageli who has made this genus 
the subject of close study, says : — ' If an attempt is made to unite into a single 
species all the types which are connected by perfectly fertile transitional forms, we 
should find only three species of native Hieracia, which have been erected by some 
authors into distinct genera : — Pilosella (Piloselloidese), Hieracium [Arc hieracium), 
and Chlorocrepis {H. staticifoliurri). Between these three groups we have, at least 
in Europe, no transitional forms ; hybrids between Piloselloideae and Archieracium 
^ See Darwin, /. c. vol. I. p. 365, and Metzger, /. c. p. 207. No great value with reference to 
variation and the constancy of varieties must be set on the result of experiments on cultivated plants, 
since the possibility of hybridisation was not excluded. Some varieties of Maize appear to hybridise 
with difficulty. 
2 Further material will be found collected in Darwin's and Metzger's works already quoted, and 
in De Candolle, Geographie botanique, Paris 1855. 
^ [H. Hoffmann gives in the Bot. Zeit, for April 27 and May i, 1874, an account of an inter- 
esting series of experiments on the extent to which the characters which distinguish the allied 
species Papaver Rhceas and dubium and Phaseolus, vulgaris and inultiflorus can be made to vary by 
cultivation, and on the tendency of the cultivated varieties to revert to the parent-form. See also 
his 'Rückblick auf meine Variations- Versuche von 1855-1880,' Bot. Zeitg. 1881.] 
* Sitzungsberichte der kön. bayer, Akad. der Wiss. March 10, 1866. 
