BULLETIN 1087, U. S. DEPARTMENT OF AGRICULTURE. 
gions because of the protection afforded to dormant or resting buds. 
However, artificial protection by means of straw has been found to 
reduce the mortality of nonhardy plants only slightly under severe 
winter conditions. This would seem to indicate that cold resistance 
is an inherent characteristic and is dependent only to a slight degree 
on the soil protection that is afforded the resting buds. It is the 
purpose of this bulletin to present data showing more definitely the 
root characteristics assumed by 'representative varieties of alfalfa 
under stated field conditions for the relation they may have in the 
adaptation to environmental conditions. The descriptions of root sys- 
tems contained herein are of the well-known varieties of alfalfa 
grown at the Eedfield Field Station in South Dakota. under conditions 
which are probably quite representative of a considerable area of 
the northern Great Plains. It is recognized that with a different soil, 
climate, and method of culture, variations may occur, but it is be- 
lieved that the general conclusions reached in this bulletin would be 
unchanged. A statement of the conditions under which the plants 
were grown is deemed desirable and is included with the other data 
presented. 
FACTORS TENDING TO PRODUCE MODIFICATIONS OF ROOT 
GROWTH. 
Root growth is influenced principally by soil, climate, cultural 
treatment, and injuries, and to a lesser degree by many other factors. 
Alfalfa is found growing under conditions of moisture from heavy 
to light precipitation; on soil types ranging from stiff, heavy clay 
to almost pure sand ; and at altitudes from below sea level to 13,000 
feet or more above sea level. Many of the alfalfas that have been 
introduced into the United States have been grown in different coun- 
tries hundreds and possibly thousands of years within compara- 
tively small areas and under peculiar soil and climatic conditions. 
It is hardly to be expected, therefore, that any one location can be 
found that will provide optimum conditions for the development 
of the root systems of all the different alfalfas. 
SOIL CONDITIONS. 
Eoot development is influenced by distribution of plant food, soil 
moisture, soil texture, water table, and hardpan or other hard mate- 
rial. Unusual soil formations in which there is a peculiar distri- 
bution of plant food may cause modifications in root growth, be- 
cause roots have a tendency to remain and develop in the areas of 
the most favorable conditions of plant food. A number of experi- 
ments have been reported showing the influence of such plant-food 
distribution on root development. 
