448 ALFALFA FARMING IN AMERICA. 
It has often been noted that as a rule isolated alfalfa plants 
set seed far more profusely than those in all but the thinnest 
stands. Observations on this point have been made in various 
parts of the Great Plains and intermountain areas and in the 
farther Southwest. On the Arlington Experimental Farm, near 
Washington, D. C., an experiment was performed to determine 
the effect of different degrees of isolation on the seed-setting 
ability of alfalfa. In this experiment, cuttings from a heavy- 
seeding plant were rooted in the greenhouse and later set out 
at varying intervals. Inasmuch as these plants were propagated 
vegetatively from the same mother plant, they did not show the 
individual variation mentioned above that would have entered into 
the experiment had seedling plants been utilized. 
The plants occupying a space equivalent to a 7-inch square pro- 
duced a maximum of 38 pods, while those having at their com- 
mand a space equal to an 11-inch square produced a maximum of 
96 pods. The highest number of pods formed on plants grown in 
rows 39 inches apart and 18 inches apart in the rows was 505. 
It will be noted that the yields were in almost direct proportion 
to the areas occupied. However, it was evident that the plants 
having the greatest distance between them had not utilized fully 
their allotted space. This was accounted for by the fact that it 
was their first season’s growth. An adjoining two-year-old cutting 
from another plant of similar seed-producing tendencies produced 
2,080 pods, and this without utilizing all of the space of 18 inches 
in the 39-inch row assigned to it. Although part of this difference 
may have been due to inherent capacity, the chief explanation for 
it must be sought in the firm establishment of the plant and its 
greater maturity. 
Just why the isolation of plants increases the production of seed 
has not been fully determined, but it is apparent that one of the 
factors involved is the increased amount of sunlight available to 
the plant. It has often been observed that trees grown on the 
banks of irrigation ditches in alfalfa fields or along the margins 
of fields always interfere with normal seed production as far as 
the influence of their shade extends. In the course of an experi- 
ment on the seed setting of alfalfa it was found that partial shad- 
ing materially reduced the quantity of seed produced by plants 
not already receiving more than the optimum amount of sunlight. 
When alfalfa plants have sufficient space for full development 
they have approximately equal illumination on all sides. With 
the plants so far apart that when fully developed they barely 
occupy the ground the potential seed-producing surface exposed 
on an acre is nearly double that of a thick stand. In the latter, 
