396 GENETICS IN RELATION TO AGRICULTURE 
Stuart in 1911 conducted a tuber-unit experiment with some 150 
standard commercial varieties of potatoes. 
“The seed used was grown in Burlington, Vt., in 1910, on land which had not 
grown a cultivated crop of any kind for at least 35 years. In addition to 
this the seed was selected from the most promising hills at the time the 
crop was harvested. The tubers as a whole were remarkably uniform in 
size and there could, therefore, have been little difference in the size of 
the seed pieces used. Any variation, therefore, which occurred between the 
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Fic. 163.—Strong and weak tuber-units of the Gold Coin variety of potatoes. Nos. 1 
and 2 represent strong and weak tuber-units in 1911; Nos. 3 and 4 represent yields from 
tuber-units 1 and 2; Nos. 5 and 6 represent yields in 1912 from 5 tuber-units of Nos. 3 and 
4. (After Stuart.) 
plants of the various tubers which were planted would seem to be due to 
some inherent tendency in the tuber itself. The remarkable dissimilarity 
between the growing plants of the individual units of a variety planted 
contiguously in the row was so surprising that some three dozen units were 
photographed and when these were harvested the tubers were also photographed 
(see Pig. 163). It was found that the divergency in yield was just as great as 
in the size and vigor of the plants. In 1912 five units were planted from both 
strong and weak plants, and it was found in practically every instance that the 
low-yielding 1911 plants gave poor germination, a feeble vine growth and a still 
lower yield than in 1911.” 
There have been many experiments similar to the one above de- 
scribed and they certainly indicate that a certain proportion (from 5 to 
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