82 cS ORIGIN OF SPECIES. 



enveloping the grains, is the primitive form ; if it is not, then no plant is now known 

 which can be considered as the ancestral form of our numerous and extremely diverse 

 varieties of maize. In this case also continued cultivation has increased the amount 

 of difference between the different varieties, as well as to a prodigious extent that 

 between them and the primitive form ; and the separate varieties are distinguished 

 from one another by a number of different characters. Some are only i^ feet high, 

 others as much as 15 to 1 8 feet; the grains stand on the rachis in rows varying from 

 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- 

 recdy 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 time 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 as with cultivated plants dissimilar forms are connected 

 by a series of intermediate forms, just as we find to be the case between the primitive 

 forms of cultivated 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 extraordinarily numerous forms, for example, of the widely distributed genus 

 Hieracium present phenomena similar in many respects to those of culdvated gourds, 

 cabbages, &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 



^ See Darwin /. c. vol. I, p. 365, and Metzger I.e. 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. 



3 [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 dtibunn and Phaseolus vulgaris and multifloriis can be made to vary by cultivation, 

 and on the tendency of the cultivated varieties to revert to the parent-form. — En.] 



* Sitzungsberichte der kon. bayer, Akad. derWiss. March 10, 1866. 



