NATURE OF CONTINUOUS VARIATION 525 
preserved specimens of each generation. At the same time he 
also carefully observed plants in the field, and, when one was 
found that showed extraordinary features, the experimental 
method was applied to it. He was especially interested in vari- 
ations, and his most notable contribution is on this subject. 
He demonstrated by his painstaking work that there are two 
kinds of variations — continuous or fluctuating and discontinu- 
ous or saltative variations. Discontinuous variations are also 
called mutations and are those extreme variations which sud- 
denly arise and remain fixed, that is, they are transmitted to 
succeeding generations. 
Nature of Continuous Variation. — Continuous variations are 
the most common kind of variations. They are simply the fluc- 
tuations that individuals show in size, shape, color, and other 
characters. Thus red flowers vary in degree of redness, leaves 
vary in shape and size, seeds vary in number per pod as well 
as in shape and size, plants differ in height, shape, method of 
branching, and so on. Continuous variations are chiefly due 
to differences in the environment, such as differences in sun- 
light, food and water supply, temperature, and influences ex- 
erted by one organism upon another. According to the work 
of De Vries and other investigators, they are not inheritable 
and, therefore, are constantly changing with the conditions that 
cause them. They fluctuate around a mean or average which 
remains practically constant, and, above or below this average, 
the individuals varying gradually grow less in number as vari- 
ability departs more and more from the average until a limit 
in each direction is reached. Continuous variations follow the 
law of Quetelet, the Belgian anthropologist, who found that 
variability follows the law of probability. Small divergences 
from the average are numerous, while larger ones are less numer- 
ous, and the larger the less numerous they are. If, for example, 
a bushel or any quantity of ears of Corn are separated into 
piles according to length, there will be one length which will 
include the greatest number and, above or below this length, 
which is known as the average, the piles will decrease in size 
as the length of ears in each pile are greater or less than the 
average. ‘This is well illustrated in Figure 469 in which 82 ears 
of Corn with extreme lengths 4.5 and 9 inches are arranged in 
10 piles according to size. ‘The same fact is illustrated in Figure 
