656 PHARMACEUTICAL BOTANY 
4. VARIATION AND Herepity.—The individuals of a species 
are not all alike and among the offspring of the same parents there 
are always at least slight variations. These variations are con- 
tinuous or fluctuating in character. 
5. Natura SELecTion.—Through the struggle for existence 
there is a natural selection which results in the survival of the 
fittest. Darwin argued that in this biological competition some 
organisms and species: possess advantageous variations and are 
consequently preserved while 
the less fortunate perish. The 
favorable characters are handed 
) down to the descendant, genera- 
tion after generation, so long as 
| they continue to be advanta- 
| geous. Thus, the weak and 
| poorly adapted organisms are 
eliminated while the forms most 
| in -harmony with their environ- 
| ment survive. 
6. ORIGIN OF SPpECIES.— 
| According to Darwin, if certain 
members of a given group adjust 
themselves to the conditions of 
Fig. 488.—August Weissmann. life through variation in one 
(Atwood.) 
direction and others in other 
directions, then divergence among the forrhs through the con- 
tinued action of Natural Selection generation after generation 
must in the course of time be sufficient to make them rank as 
separate species. 
WEIssMANN’S GERM PLAsm THEORY.—August Weissmann 
(1834-1914), a German biologist, developed a theory of heredity 
based upon the principle of the continuity of the germ plasm. 
While this principle was recognized earlier by Owen (1849), 
Galton, Nussbaum and others, it remained for Weissman through 
a series of brilliant essays and a book on the Germ Plasm (1892) 
to bring it forcibly to the attention of scientific world. 
Weissmann vigorously denied the inheritance of all forms of 
acquired characters. He believed (1) that the cells of an 
