NORTHERN GREAT PLAINS FIELD STATION, 1913-1922 27 
those two winters were unusually mild, so accurate comparisons can 
not be made. 
In order to compare more accurately several planting systems, 7 
experimental blocks of equal area were planted in 1921, the same 
varieties of apples and plums being used in all blocks. In blocks 1 
and 5 plums are in rows 15 feet apart with the trees spaced 6 feet in 
the row, and apples are in rows 20 feet apart with the trees 6 feet 
in the row. In blocks 2 and 6 plums are spaced 15 feet square and 
apis 15 by 20 feet. In blocks 3 and 7 plums are planted in groups 
of four with the groups spaced 15 by 20 feet, and apples in groups of 
four with the groups spaced 20 by 20 feet. The four trees in each 
group are spaced about 214 feet apart. In block 4 plums and apples 
are planted in the hexagonal system, the plums 12 feet and the 
apples 1614 feet apart. Standard varieties of known hardiness were 
used in this experiment. Apples are on the hardy Pyrus baccata 
roots, crabs on their own roots, and the plums on Prunus Americana 
roots. Notes will be taken to show the effects of the different plant- 
ing systems on winter injury, growth, yields, quality of fruit, and the 
longevity of the trees. Good stands were obtained, except with one 
plum variety. , 
TREE FORM AND PRUNING 
An experiment was started in 1915 with several sand cherry—plum 
hybrids to compare the results with these fruits grown in tree form 
and in bush form. Observations indicate that the bush form is the 
more satisfactory. These hybrids naturally grow in bush form. 
No definite experiment has been carried out to compare high- 
headed and low-headed trees, but observations made on many trees 
indicate that low heading is the more desirable. Whether the tree 
should branch at the surface of the ground and grow in bush form or 
whether the lowest branches should be from 6 to 18 inches from the 
ground remains to be determined. 
But little experimental work in pruning has been attempted, very 
light pruning generally having been employed with all tree fruits. 
Small fruits have been pruned in the standard way. 
A few Opata and Sansoto plums planted in 1914 were pruned 
lightly, moderately, and severely in the autumns of 1920 and 1921. 
Both moderate and severe pruning reduced yields the following years, 
although the grade and size of the fruit were somewhat improved. 
As far as could be seen, the pruning had no effect on hardiness. 
Karly results are decidedly in favor of the light pruning on account 
of the heavier yields. 
To get more information on pruning and its relation to hardiness 
and fruit bearing six blocks of fruit trees were planted in 1921. Two 
blocks receive very light pruning, the trees being allowed to grow 
naturally except for removal of dead and broken limbs. Two blocks 
receive moderate pruning. In these blocks an attempt is made to 
select the main limbs and shape the tree. Further pruning consists 
of a light thinning out of the superfluous limbs to admit light and 
the removal of dead, broken, or interfering limbs. The trees in the 
other two blocks are pruned severely. They are treated the same as 
the moderately pruned trees except that thinning out of superfluous 
branches is a little more severe and part of the annual growth is 
