298 BOARD OF AGRICULTURE. 



plants by liybridizatioii and cross-breeding. True hybrids or 

 mules are produced when the ovules of one species are impreg- 

 nated by the pollen of another, and seeds thus obtained which 

 are capable of germination and complete development as plants. 

 Cross-breeds result from the blending of mere varieties of plants 

 of the same species, which occurs often by accident, as observed 

 in the mixing of different varieties of Indian corn, when grow- 

 ing in the same neigliborhood. While the production of hybrids 

 is more or less difficult, even between closely allied species, and 

 the seeds obtained often few in number and but feebly endowed 

 with vitality, cross-breeds are produced with the greatest facility. 

 Hence the constant tendency to deterioration and change in 

 the varieties of garden vegetables, since it is impossible to raise 

 pure seed of more than one variety of any species in the same 

 vicinity, unless they blossom at different periods. 



The difficulty of obtaining true hybrids is illustrated by the 

 fact that only 259 were procured as the result of 10,000 experi- 

 ments carried on during many years by Gacrtner, the highest 

 authority upon this subject. He found it impossible to form 

 hybrids between many closely allied species, as between the cur- 

 rant and the gooseberry, the blackberry and the raspberry, and 

 the pear and the apple. He also was unable to discover any 

 definite law respecting " the relative influence of the parent 

 species, sometimes the characteristics of one and sometimes of 

 the other being most predominant in the hybrid. The majority 

 of hybrid plants liavc not the power to develop perfect seeds, 

 but, like the mules of the animal kingdom, are sterile, and 

 therefore can only be propagated by extension. Moreover, the 

 seeds ripened by hybrids are usually formed in the earliest and 

 most vigorous flowers which open, while the later flowers are 

 barren ; and such seeds often germinate into plants, which may 

 be called still-born, since they inevitably perish when the nourish- 

 ment laid up in the seed is exhausted. In the few cases where 

 hybrids produce perfect seeds freely for several generations, the 

 plants revert in character to one or the other of the original 

 species; and, if a hybrid be crossed with one of its parent 

 species, seeds are yielded in abundance which develop into 

 plants with the characteristics of that parent. 



Tlio principal obstacle to be overcome in hybridizing species 

 capable of crossing arises from the extraordinary power of the 



