30 
Colorado Experiment Station. 
whole crops are destroyed by tlie yellows, a Fiisariiun disease, and 
the lands stay sick to cabbage for an unknown number of years. 
VI. THE HOPE OF DISEASE-RESISTANT POTATOES. 
Among cabbages there are found a few that dO' not have the 
disease and their seed produces plants most of which do not have 
the disease, as the author has shown in Muscatine county, following 
the work of Dr. L. R. [ones, in the Racine district of Wisconsin, 
To have an equal chance of finding such plants among potatoes, a 
vast number of seedlings would have to be produced, and in the 
Greeley district practical!}^ no seed is borne except by the Pearl 
bastard. If, among many hundreds of thousands of its seedlings, 
a goodly number of resistant plants were found, it might be possible 
to find one worthy to use as the commercial variety ol the district, 
but all these seedlings and all the seed stock of any worthy variety 
would have to be produced elsewhere under better conditions for 
health and then be brought to the regions of greater strain upon 
health in potatoes. The price o<f a small battleship would be required 
to carry on breeding work on a scale vast enough to promise success 
under such difficulties. 
VIL SUMMARY. 
Leaf-roll, regarded as the sum of ill health for potatoes in 
Colorado, appeared widely and suddenly in 1911, continued in 1912, 
1913 and 1914, and disappeared in 1915. 
Soils in the Great Plains region may reach dangerous temper¬ 
atures in years of more than average sunshine. Potatoes were 
found badly injured in good, but overheated, potato soils, but 
heated air, constantly changed, seemed to add very little to the ill 
health of the plants. 
In 1911, temperatures for the critical month of June, for the 
whole upper foot of soil, averaged, in the locality most affected, 
10° more than in June, 1910. In other regions there was much 
injury from over soakage of potato lands. 
Potato roots use as much as four feet of suitable soil, but do not 
enter very close-grained soils, and die in wet soils. The potato root 
cap offers additional evidence that potato roots have the power 
neither to enter nor to live in close-grained, easily wet, and poorly 
aerated soils. The structure of the potato leaf and practical obser¬ 
vations indicate that a damp atmosphere is best for potatoes. 
Potato plants grown under controlled soil temperatures and 
percentages of moisture ga^T evidence that soil heat and soakage 
