206 ESSENTIALS OF BOTANY 



hardship than the ones which die. In this way delicate 

 individuals are weeded out and those which are more 

 robust survive. One shellbark hickory bears nuts whose 

 shell is easily cracked by hogs, while another protects its 

 seeds by a shell so hard that it is cracked only by a pretty 

 heavy blow. In case of all such differences, there is a 

 strong tendency to have the less eatable fruit or seed 

 preserved and allowed to grow, while the more eatable 

 varieties will be destroyed. The result of this kind cf 

 advantage, in any of its countless forms, is sometimes 

 called survival of the fittest, and sometimes 7iatural selec- 

 tion. The latter name means only that the outcome of 

 the process just described, as it goes on in nature, is much 

 the same as that of the seed grower's selection, when, by 

 picking out year by year the sweetest sugar-beets or the 

 most nearly " stringless " beans, he obtains permanent 

 new varieties. To obtain new species, though possible, 

 would be more difficult, for these are divided from each 

 other by greater differences than those which distinguish 

 varieties from varieties (Sects. 256, 258). It has recently 

 been proved by Professor Hugo de Vries, of Amsterdam, 

 Holland, that while all plants, from generation to genera- 

 tion, show variations, sometimes -they show mutations as 

 well. A mutation is a sudden, marked change, a sort of 

 leap, such as the growth of pecan trees from hickory nuts or 

 of pansies from the seed of common blue violets would be. 

 None of the observed mutations in plants have been as con- 

 spicuous as those above suggested, but to the botanist they 

 are quite as remarkable. Since new species produced by 

 mutation continue to reproduce themselves, many species 

 may, in the course of ages, have been thus produced from 

 a few ancestral forms. 



