924 
ORIGIN OF SPECIES. 
I'ulgare laceratum and S. 'vulgare Crista-galli, 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 communis, 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 ; 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, I. c. vol. II. p. 379. 
Also Nägeli, Sitzungsberichte d. k. Layer. Akad. d. Wiss. 1866, p. 274. 
^ See Metzger, Landwirthschaflliche Pflanzenkunde, Frankfurt a. M. 1851, p. 1000; and 
Darwin, /. c. vol. I. p. 323. 
