GENETICS AND EVOLUTION : 653. 
called fluctuations. (2) Variations due to new combinations of ances- 
tral characters which in some cases were latent in the parents 
but present in the grandpabents or in more distant ancestors. 
Such instances are called ‘‘reversions.”’ (3) Mutations or sudden 
and frequently large differences which appear among individuals 
not of hybrid origin. It is believed that many varieties of 
economic plants had their origin in seed mutants or “sports.” 
The mutations seen in plants reared from seed sports are due to 
hereditary causes in which there probably occur a combination 
of parental characters. Bud mutations or bud sports sometimes 
occur on normal plants as in some varieties of fruit trees espe- 
cially in certain citrus fruits. The Boston Fern, Nephrolepsis 
exaltata bostoniensis is a bud sport of Nephrolepsis exaltata. This 
form of mutation is due either to the alternation of a simple gene 
in a certain chromosome or to abnormalities in the distribution of 
the chromosomes during mitosis. Continuous variations are small 
additions or diminutions of certain parental characters. Dis- 
continuous variations are sudden marked variations which arise 
without the appearance of transitional stages, as for example 
where variations occur in the normal number of parts, as in the 
four-leaved clover. De Vries called these kinds of variations 
mutations. 
EVOLUTION 
Organic evolution is the established fact that all forms of 
organisms existing today have been derived from others pre- 
viously existing either by direct descent or common ancestry. 
It did not originate with Charles Darwin. It was first conceived 
by Anaximander, Empedocles and other ancient Greeks. ‘The 
more important theories as to the method of evolution will now 
be discussed. 
THe LAMARCKIAN THEORY OF Use AND DisusE.—Jean 
Baptiste de Lamarck (1744-1829) a French naturalist, pro- 
pounded his theory on the origin of species in 1809 in his “Phil- 
sophie Zoologique.” He assumed that the environment changes, 
that use and disuse may alter the character of the individual, 
that characteristics acquired by an organism in its lifetime are 
inherited by its offspring. The persistent use of a part of the 
