The Colorado Potato Industry. 
21 
ably in their habit of growth. Tubers are borne on root stocks 
or under ground stems that always grow from the stem of the 
plant above the old seed tuber. Figures 3, 1 and 2, Plate VI, show the 
characteristic habit of growth of Pearl, Rural N. Y. No. 2 and 
Improved Peachblow. The Pearl sends out short root stocks just 
above the old seed so that the tubers are formed closely around the 
center of the hill and at about the depth that the seed is planted. 
Rural N. Y. No. 2 has a longer rootstock and is apt to start high¬ 
er above the old seed so that the tubers are more scattered in the 
hill. Some of them are deep in the soil and others will be close 
to or at the surface of the ground. The Improved Peachblow is 
still more irregular in its habit of tuber growth. These peculiar 
habits of growth make less difference under the hilling system of 
culture employed in the irrigated districts than where the level 
system is practiced. 
With most machines the seed is planted too shallow rather 
than too deep. Many potatoes that are supposed to be planted 
four or five inches deep are really not more than one or two in¬ 
ches under the level surface of the soil. If the soil is sufficiently 
moist this does no harm but if the soil is dry at the surface, a poor 
stand is apt to result. 
ROTATION OF CROPS AND RHIZOCTONIA 
The rotation of crops as practiced in this state does not tend 
to lessen the amount of disease. The Rhizoctonia which causes 
the blight and a greater part of the scab of potatoes works on al¬ 
falfa as well as potatoes. So far as is known the disease does not 
live on the cereals so that is has been suggested that if potatoes 
could be preceeded by wheat or oats, instead of alfalfa, the amount 
of the disease might be lessened. The efficiency of a rotation of 
this kind is doubtful, however, as it is probable that the disease 
lives in the soil more than one year without any host plant, more¬ 
over the loss of the beneficial effects of alfalfa upon the soil would 
possibly be more than the ordinary loss from the disease. 
SELECTION 
A large part of the improvement in plants has been brought 
about through selection. This applies to plants propagated by 
vegetative parts as well as those propagated by seed. All the do¬ 
mesticated species are originated either from crossing or varia¬ 
tions and are fixed in their particular characteristics by selection. 
The different varieties of a species may be called the variations of 
that species. When a variety is planted year after year it is sure 
