juiy 14,1923 Degeneration Diseases 0} Irish Potatoes 93 
greater or less than the sum of the effects of both considered separately. 
With a given yield rate, the quality may be affected with a loss depending 
somewhat on the demands of the trade regarding the characteristics of 
the tubers or progeny. 
ADVANTAGES TO BE DERIVED FROM CONTROL 
Table XXIV summarizes the results of a number of yield tests that 
have been made with parts of the same strain in each of two varieties. 
The L strains secured on the L farm will be discussed first. In 1918, on 
Aroostook Farm, the yield rates were reduced by an all-mosaic condition 
(mild type) slightly more for Bliss Triumphs than for Green Mountains 
in comparison with plots with part of the hills—the mosaic ones— 
removed during the season. In 1919, on Aroostook Farm, the yield rates 
were reduced by an all-mosaic condition much more for Bliss Triumphs 
than for Green Mountains, in comparison with plots with about a fifth 
of the hills mosaic. In 1920, on a field with poor soil and cultural condi¬ 
tions, the yield rates were reduced less by an all-mosaic condition for 
Bliss Triumphs than for Green Mountains, in comparison with plots with 
about a fifth of the hills mosaic. In 1919, the only year of the three in 
which conditions were at all normal and favorable for growing potatoes 
and for making such a test, for each 10 per cent of mosaic the reduction 
amounted to 2.8 barrels 4 an acre for Green Mountains and to 5 barrels for 
Bliss Triumphs. 
In these two strains and in many small lots (40, p. 316) the writers 
have not observed an increase in severity in symptoms except in some 
cases where another disease, such as the spindling-tuber disease, came in 
or increased, as in the following tests. In 1921, on Aroostook Farm, the 
same Green Mountain stock mentioned above was again used for yield 
tests. One part about a third mild mosaic and a third spindling tuber, 
both first-year symptoms following infection late in 1920, had a yield 
rate of 146 barrels an acre. A part all mild mosaic, as for several years 
at least, and about a third spindling tuber (first-year symptoms) had a 
yield rate of 96 barrels. Another part all mild mosaic, as for several 
years, and all spindling tuber with the second-year symptoms (third year 
of disease) had a yield rate of 68 barrels. 
Comparing the first and second parts gives a reduction of about 7 
barrels an acre for each 10 per cent of mild mosaic, while comparing the 
second and third parts gives a reduction of about 4 barrels an acre for 
each 10 per cent of spindling-tuber disease in mild mosaic stock. In 
these tests the size of the plots varied from one-fifth to one-fourth of an 
acre in 1918 and 1919, from one-ninth to one-fifth in 1920, and from one- 
eleventh to one-sixteenth in 1921. 
Further comparisons in Table XXIV lead to the following conclusions: 
The mosaic part of a strain sometimes yielded less than a partly rogued 
healthy part, as in Green Mountain strain L (1918,1920), in Bliss Triumph 
strain L (1918, 1919, and 1920), and in Green Mountain strain S (1920). 
The mosaic part of a strain sometimes yielded more than a rogued healthy 
part but only so if the allowance is not made for loss by roguing, as in 
Green Mountain strain L (1919), strain S (1918 and 1919), and strain W. 
The mosaic part of a strain sometimes yielded less than an unrogued 
healthy part, as in Green Mountain strain L (1919; 1920 on P farm; 
4 A “barrel” (barrelful) is 165 pounds, or 2H bushels. 
