76 ON CROSSING AS A" CAUSE Chap. XV. 



regard to crossed varieties of plants, Mr. Beaton remarks ^^ 

 that " Melville's extraordinary cross between the Scotch kale 

 and an early cabbage is as true and genuine as any on record ;" 

 but in this case no doubt selection was practised. Gartner ^* 

 has given five cases of hybrids, in which the progeny kept 

 constant ; and hybrids between Dlanthus armeria and deltoides 

 remained true and uniform to the tenth generation. Dr. 

 Herbert likewise showed me a hybrid from two species of 

 Loasa which from its first production had kept constant 

 during several generations. 



We have seen in the first chapter, that the several kinds 

 of dogs are almost certainl}'" descended from more than one 

 species, and so it is with cattle, pigs and some other domesti- 

 cated animals. Hence the crossing of aboriginally distinct 

 species probably came into play at an early period in the 

 formation of our present races. From Eiitimeyer's observa- 

 tions there can be little doubt that this occurred with cattle ; 

 but in most cases one foim will probably liave absorbed and 

 obliterated the other, for it is not likely that semi-civilized 

 men would have taken the necessary pains to modify by 

 selection their commingled, crossed, and fluctuating stock. 

 Nevertheless, those animals which were best adapted to their 

 conditions of life would have survived through natural 

 selection ; and by this means crossing will often have in- 

 directly aided in the formation of primeval domesticated 

 breeds. Within recent times, as far as animals are concerned, 

 the crossing of distinct species has done little or nothing to- 

 wards the formation or modification of our races. It is not yet 

 known whether the several species of silk-moth which have 

 been recently crossed in France will yield permanent races. 

 With plants which can be multiplied by buds and cuttings, 

 hybridisation has done wonders, as with many kinds of Eoses, 

 Rhododendrons, Pelargoniums, Calceolarias, and Petunias. 

 Nearly all these plants can be propagated by seed, most of 

 them freely ; but extremely few or none come true by seed. 



Some authors believe that crossing is the chief cause of 

 variability, — that is, of the appearance of absolutely new 



'^ ' Cottage Gardener,' 1856, p. ^* ' Bastarderzegung,' s. 55-3. 



110. 



