248 A TEXTBOOK OF GENERAL BOTANY 
PLANT BREEDING 
Selection. The method of obtaining improved varieties has 
been that of selecting plants with desired characters for propa- 
gation, and discarding undesirable ones. Of course, the act of 
selecting individuals with desirable characters cannot produce 
anything new, as selection presupposes variations which can be 
selected. In order to learn how new varieties are produced it 
is necessary, therefore, to consider the origin of variation. Vara- 
ation is a universal phenomenon among both plants and animals, 
—so universal, in fact, that it has given rise to the common 
expression that no two plants or animals are alike. 
Acquired characters. Favorable methods of cultivation fre- 
quently result in the production of larger and more vigorous 
individuals. If a plant attains to an exceptionally large size 
by growing under unusually favorable conditions, this size is 
said to be an acquired character, as it is one acquired during 
the life of the individual and not one that the individual in- 
herited. Such acquired characters do not appear to be inherited. 
The seeds of vigorous plants are likely to be larger than those of 
weak plants; large seeds contain more stored food than smaller 
ones, and so give the seedlings a better start. In this way the 
offspring of a vigorous plant may be somewhat larger than the 
offspring of a less vigorous one. This character, however, is not 
hereditary, as the larger size will be maintained only so long as 
each generation is grown under the favorable conditions that 
gave rise to this exceptional vigor. 
Continuous variations. The variations between plants are of 
different kinds. Some are minor variations, known as continu- 
ous variations, which are not inherited. When many plants 
of one homozygous variety are examined, it is found that they 
differ from one another by slight variations which are quanti- 
tative in character and do not depart from the average beyond - 
a certain limit. Thus, some plants will be shorter and others 
taller, some will have deeper-colored and others lighter-colored 
flowers, etc. While the plants of one generation may vary thus 
