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IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
a genus that he chose for working with because of the enormous 
number of forms under which it naturally exists. 
By crossing together the more distinct varieties, he evidently 
hoped to produce some of these numerous wild forms, and so 
throw light upon their origin and nature. In this hope he was 
dissappointed. Instead of giving a variety of forms in the F 2 
generation, they bred true and continued to do so as long as they 
were kept under observation. More recent research has shown 
that this is due to a peculiar feature known as parthenogenesis 
and not to any failure of the characters to separate clearly from 
one another in the gametes. Mendel, however, could not have 
known of this, and his inability to discover in Hieracium any in- 
dication of the rule which he had found to hold good for both 
peas and beans must have been a source of considerable disap- 
pointment. Whether for this reason or owing to the utter neglect 
of his work by the scientific world, Mendel gave up his experi- 
mental researches during the later part of his life. His closing- 
years were shadowed with ill health and embittered by a con- 
troversy with the Government on a question of the rights of his 
monastery. He died of. Bright’s disease in 1884. Mendel’s ex- 
periments, published in 1866, remained unnoticed until the facts 
were rediscovered in 1900 by DeVries , Correns and Tschermak. 
THE MUTATION-THEORY OF DEVRIES 
Hugo’ DeVries, director of the Botanical Garden in Amsterdam, 
has experimented widely with the growth of plants, especially the 
evening primrose, and has shown that different species appear to 
rise suddenly. The sudden variations that breed true, and thus 
give rise to new forms, he called mutations, and this indicates 
the source of the name applied to his theory. 
In his “Die Mutations theorie,” published in 1901, he argues 
for the recognition of mutations as the universal source of the 
origin of species. Although he evokes natural selection for the 
perpetuation and improvement of variations, and points out that 
his theory is not antagonistic to that of natural selection, it is 
nevertheless directly at variance with Darwin’s fundamental con- 
ception — that slight individual variations “are probably the sole 
differences which are effective in the production of new species” 
and that “as natural selection acts solely by accumulating slight, 
successive, favorable variations ; it can produce no great or sudden 
modifications.” The fundamental idea of DeVries’ theory is that 
“species have not arisen through gradual selection, continued for 
