THE FLOWER 233 
conditions that tend to produce it. If he wishes to develop 
a dwarf variety, for instance, he will take notice that over- 
crowding, lack of nourishment, and cold tend to produce that 
result in nature, and by acting on this hint he can direct his 
efforts more intelligently. He will learn, too, not to waste 
time in trying to breed a plant contrary to its nature. He 
must not expect to gather figs from thistles by any art of 
selection or skill in culture. By attention to Mendel’s law, 
a still further saving of time and labor may be effected. 
It is obvious, from what has been said, that a breeder’s 
chance of finding what he wants will be greater in proportion 
to the number of individual plants he has to choose from. 
For this reason, a horticulturist sometimes uses thousands 
and hundreds of thousands of specimens of a single kind in 
conducting his experiments. In this way he compresses into 
a short space of time the advantage that nature can gain only 
by spreading her random experiments over a long series of 
years, or even centuries. 
264. Mutation and variation. — There are at least two 
ways in which changes in vegetable and animal forms are 
thought to occur: (1) 
by the preservation and 
fixation through selec- 
tion and heredity, of 
slight differences that 
may appear from time to 
time, such divergences 
being called “ fluctuat- 
ing variations” ; (2) by 
the appearance now and 
then, due to causes as 
. Fie. 340.— Mutation in twin ears of corn, 
yet unknown, of definite showing the sudden variations that sometimes 
occur, by which a new type may be provided 
and sudden changes without the labor of selection. 
creating a new form at 
a single, though perhaps small, leap. When such a change 
is temporary and passes away with the individual in which 
