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 natural 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. 
