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IOWA ACADEMY OF SCIENCE Vor,. XXIX, 1922 
duced them, and that without other action than that of their own 
proper pollen, under such conditions that the pollen of the parents 
is not able to exercise the influence to determine this return.” 
In 1864 Naudin communicated a second report to the Academy, 
in which he confirmed his previous results as to uniformity in 
the first generation crosses, the identity of reciprocal crosses, and 
the “disorderly variation,” as he calls it, of the hybrids of the 
second and succeeding generation. In neither of the two papers 
is there any numerical classification of the hybrid types. 
Naudin’s memoir is often referred to as amounting virtually 
to a statement of Mendel’s law of the disjunction of hybrids. 
In Naudin’s case, however, the statement was of a speculative 
nature and consisted in the proposition of a scientific hypothesis ; 
in Mendel’s case, his “law” was a scientific conclusion derived 
as the result of experiment. Naudin propounded, in 1863, a well- 
reasoned theory of probable truth ; Mendel, in 1868, formulated 
a statement of ascertained fact. 
The work of Verlot. — in 1865, B. Verlot, of the Jardin des 
Plantes at Paris, published a brief memoir which in 1862 had 
received a prize from the Imperial and Central Horticultural 
Society, the thesis of which was as follows: “To demonstrate 
the circumstances which determine the production and fixation of 
varieties in ornamental plants.” The memoir is of interest as 
thoroughly and typically embodying the general point of view of 
the day concerning hybridization and the origin of new varieties, 
while affording at the same time much matter of interest from 
the standpoint of practical horticulture. Verlot presented the view 
that, while the causes of variation are unknown, they arise under 
definable circumstances, and the ones which he enumerates are 
prolonged cultivation, removal from one set of climatic and soil 
conditions to another, and hybridization. 
The thought of the time did not clearly distinguish a difference 
between the nature of the changes brought about by the external 
environment and those arising from sexual fertilization. Both 
were generally assumed to be equally heritable. Cultivation long 
continued was considered to have been especially potent in bring- 
ing about variation. In Verlot’s words: “It is especially with 
plants cultivated for a great number of years, with those the 
introduction of which is so ancient that it is lost in the night of 
time, that one finds profound and multiplied modifications.” 
He further voices the then prevailing view regarding the re- 
lation between culture and variation: “If we compare,” he says, 
