Improvements Made in Plants by Man 439 



It is both known from experience, and also has been shown by 

 experiment, that crossing yields more vigorous, abundant, and 

 variable offspring than in-breeding, in which fact lies the reason, 

 doubtless, why nature promotes it. In crossing, not only is va- 

 riability promoted by the introduction of the pecuharities of two 

 lines of ancestry, but the very commingling of the two strains of 

 protoplasm seems to favor the appearance of wholly new varia- 

 tions, somewhat after the analogy of these liquids in chemistry, 

 which are perfectly clear by themselves but turbid when com- 

 mingled. It appears also to be a fact that the offspring are more 

 vigorous, prohfic, and variable yet, if the two plants between 

 which the cross is made are not raised side by side under the 

 same conditions, but apart and under somewhat different condi- 

 tions. Cross pollination between plants thus grown is something 

 which nature cannot provide for, but man can, and sometimes 

 does, as when he plants seeds in alternate rows treated somewhat 

 differently in cultivation. By this method man can intensify 

 variation, and thus provide a wider and better basis for selection. 

 (4) He can pollinate a given stigma by pollen from a plant of 

 another variety of the same species. This is called hyhridization 

 in both Botany and Horticulture, though by some it is also desig- 

 nated crossing. Occasionally no result follows, but usually seed 

 sets and will grow into new plants which breed freely together. 

 The first generation of such hybrid progeny exhibit characters de- 

 rived from both of the original parents, and are likely to be more 

 vigorous than those parents; but (and this will be news to many 

 of my readers), these characters are not combined in the same 

 way in all of the descendants of those hybrids, though the ways 

 are very definite. This very important matter, which involves a 

 notable natural law discovered by Mendel and known by his name, 

 has already been considered in the chapter on Reproduction, and 

 it will suffice to recall here that the characters of the original 

 parents are inherited by the descendants of hybrids as definite 

 entities in definite mathematical proportions. This fundamental 



