10 
Colorado Experiment Station 
To make the best use of water and to delay air exclusion, if pos¬ 
sible until the cooler weather of late July and August, irrigation is 
put off until the plants show considerable signs of suffering for water, 
or until in most cases after the first blossoms have opened and the 
tubers set. In most seasons there is moisture about the lower roots 
sufficient to sustain the plants, but as no rains come, there is not 
moisture enough above the seed piece, and no tubers are set until 
well into August, because tuber stems do not start unless moisture 
is in actual contact with the main stems. This is the chief reason 
for hilling potatoes—to more thoroughly mulch the soil about the 
main stems, and is said to have been discovered in Germany in the 
early days of potato culture there. It is one of the basic principles 
of potato growing. 
Thus in the Greeley system the deep close cultivation tears off 
side roots, dries out the soil, and reduces the food supply at and prior 
to blossoming time. A well known scientific law which applies both 
to animals and as here to plants has been formulated by Doctor J. C. 
Arthur of Purdue University as follows: “A decrease of nutrition 
during the period of growth of an organism favors the develop¬ 
ment of the reproductive parts at the expense of the vegetative parts.” 
With this fact all the farmers are familiar in its application to farm 
animals, and, in Colorado, growers of wheat and of alfalfa for seed 
production know that the withholding of water at a certain stage of 
growth increases the set of seed. 
Associated at Greeley with methods that reduce the supply of 
available food at the budding and blossoming season, we have an un¬ 
natural delay .of tuber formation, and the use of food therefore, fol¬ 
lowed, when irrigation at last commences, by the instant availability 
of a large food supply. Thus we have all the requisites for variation* 
of the plant in all its parts at the time of tuber growth in the direction 
of any impulse given it by previous conditions. Disease is also a 
large factor, often the largest factor, in potato plants tending toward 
going to seed. Often when the underground stems and tuber stems 
are attacked, especially in rich conditions, by fungous disease, there 
is induced a trouble called in Colorado “Little Potatoes.” The promi¬ 
nent symptoms of this disease are the growth of large vines and many 
and large side branches, and the formation above or just below the 
ground of many small knotty tubers. These side branches 
blossom profusely, even when grown from tubers borne by prolific 
non-blossoming plants, but do not appear, the first season, to bear 
pollen. 
Abundant food supply is recognized by plant breeders as promoting or 
allowing variation, reversion, or “sporting;” and wild plants are considered to 
be more stable and uniform in their characteristics because struggling in 
nature with other plants for food, they are less richly nourished than when 
cultivated by man and thus favored, protected and allowed to develop freely 
their inherent qualities. y y 
