924 ORIGIN Of" SPECIES, 



'vulgare laceratum and S, 'vulgare Crista-gaUi, which was of the normal form, uniformly 

 produced plants of the normal parent-form, while those produced on the outer abnormal 

 part of the leaf reproduced the special varieties*. 



Sect. 36. — Accumulation of new characters in the reproduction of 

 varieties. The difference between a variety and its parent-form, or between the 

 varieties of a common parent-form, is usually at first small and affects only a few 

 characters. But the descendants of the variety may again vary, the new characters 

 may thus become intensified, and other new characters of a different kind may be 

 added to them. The amount of difference between parent-form and variety and 

 between the various varieties of the same parent-form thus becomes greater ; and if 

 the tendency of the characters to become hereditary increases with the increase of 

 their difference, the variety comes at length to differ so greatly from the parent-form 

 that their genetic connection can only be proved historically or by the existence of 

 transitional forms. This is the case with many of our cultivated plants, as e. g. the 

 Pear, which varies much even in the wild state, but under cultivation has altered its 

 mode of growth, form of leaf, flower, and especially its fruit, to such an extent that 

 it would be impossible to suppose the finest sorts of Pears to be descendants of the 

 wild Pyrus cotfimunis, if Decaisne had not proved their genetic connection by the 

 study of the transitional forms (Darwin, /. c. vol. I. p. 350). In the same manner it 

 scarcely admits of a doubt that all the cultivated kinds of Gooseberry are descended 

 from the wild Ribes Grossularia of Central and Northern Europe ; and Darwin 

 brings forward historical evidence to show that the size of the fruit has been con- 

 tinually increased by cultivation since 1786, so that in 1852 it had attained the 

 weight of 895 grs. Darwin found that a small apple 6^ inches in circumference 

 weighed as much (/. c. p. 356). The different varieties of Cabbage are all descended 

 from one parent-species, or, according to Alph. de Candolle, from two or three 

 closely related ones still growing in the neighbourhood of the Mediterranean. In 

 this case hybridisation has also cooperated j the varieties are for the most part 

 hereditary but without any great constancy. The extent of the variation which has 

 taken place under cultivation is shown by the existence on the one hand of shrubby 

 forms with branching woody stems, 10 to 12 or even 16 feet high, on the other 

 hand of the round Cabbage with a short stem and a spherical, pointed, or broad 

 head consisting of leaves closely packed one over another ; and again of the Savoy 

 with its curled blistered leaves, the Kohl-Rabi with its stem swollen below, the Cauli- 

 flower with its crowded monstrous flowers, &c.^ 



In the case of many cultivated plants the original wild form is unknown. It is 

 possible that in a few cases it may have disappeared; but it is more probable 

 that the varieties which have arisen under cultivation have gradually acquired such a 

 number of new characters that their resemblance to the wild parent-form can no 

 longer be traced. This is probably the case with the cultivated Cucurbitaceae, 

 Gourds, Bottle-Gourds, Melons, Water-Melons, &c., the hundreds of varieties of which 



^ Ann. and Mag. Nat. Hist, third series, vol. VIII, 1861, p. 490 ; Darwin, /, c. vol. II. p. 379. 

 Also Nageli, Sitzungsberichte d. k. bayer. Akad. d, Wiss, 1866, p. 274. 



^ See Melzger, Landwirthschafdiche Pflanzenkunde, Frankfurt a. M. 1851, p. 1000; and 

 Darwin, /. c. vol. I. p. 323. 



