GENETICS AND EVOLUTION 657 
organism are of two kinds, the body or somatic cells containing 
somatoplasm and the germ cells containing germ plasm, (2) that 
the germ cells reside in the body but are not part of the body or 
soma, (3) that the germ cells arise as direct descendants of the 
germ cells of the previous generation, (4) that the germ plasm 
continues from the beginning of life and the soma protects it, 
(5) that variations arise from combination of different characters 
in the germ plasm of each parent, (6) that the determiners 
originate solely in the germ plasm and migrate from the germ 
cells out into the various parts of 
the developing body and that | 
differentiation of the organism is 
produced in this way, (7) that a 
new type of organism arises only 
in consequence of a changed type 
of germ cell. 
Weissmann’s ideas about vari- 
ation were just the reverse of those 
held by Lamark and Darwin who 
believed that variations first origi- 
nate in the body and are thence 
passed on to the germ cells. He pi a range 
stressed the imp ortance of heredi- of Ate of ae as @ meted 
ty in evolution but almost NC¥- of evolution. (After Walton and Foss.) 
lected environment. 
De Vries Mutation THEoRY.—Professor Hugo De Vries, 
a Dutch botanist, in 1901, advanced the theory of evolution 
through sudden abrupt variations. He asserted that new 
species arise suddenly and become fully established from a 
parent form which may continue to live side by side with the new 
form. He called these sudden variations, mutations. De 
Vries reached his conclusions from the striking variations he 
discovered in successive generations of the Evening Primrose 
(Ocnothera lamarckiana), a species he found growing wild, in 1886, 
in a waste field about Hilversum in Holland. In experimenting 
on the Evening Primrose in his Amsterdam gardens, he found the 
mutants when self fertilized proved stable, and when crossed 
behaved according to the Mendelian laws. De Vries’ principal 
