450 ALFALFA FARMING IN AMERICA. 
investigators indicate that practically no seed is produced if the 
flowers are not tripped. Bumblebees (Bombus spp.) are gener- 
ally believed to be the most efficient of all insects in setting off 
the explosive mechanism, and hence in bringing about pollination. 
Honeybees, though not nearly so effective as bumblebees, should 
not be underrated in this connection. It is a practice in some 
parts of the country to place beehives along the margins of al- 
falfa fields intended for seed. Beekeepers follow with their col- 
onies fields planted for seed, for the purpose of getting tne honey. 
This is mutually beneficial, as larger yields of both seed and honey 
result. Wild bees (Andrena spp. and Megachile spp.) and various 
butterflies are also valuable agents in pollinating alfalfa flowers. 
That the explosion of alfalfa flowers may be accomplished by 
other means than insect visitation is quite well known. The in- 
sertion of a more or less pointed instrument into the throat of the 
corolla has often been resorted to in studying the tripping 
mechanism of individual flowers. Roberts and Freeman describe 
a method of exploding flowers in large numbers by rolling the 
head carefully but firmly between the thumb and the first and 
second fingers. This trips the flowers then at the proper stage 
of maturity. Tripping on a still more wholesale scale may be 
done by grasping the entire plant between the hands at successive 
intervals. In this case it is best to work from the bottom toward 
the top of the plant, exerting the required pressure at the proper 
intervals. 
It has been found that flowers tripped by any form of manip- 
ulation set seed readily, while other flowers left unexploded and 
from which insects are excluded rarely set seed. 
As only a slight pressure on the keel is necessary to trip the 
flower artificial methods may be resorted to as a means of sup- 
plementing the natural process as accomplished by insects. In 
an experiment at the Arlington experimental farm in which the 
method mentioned of exerting pressure successively over the whole 
plant was used, the yield of pods was increased 251% per cent 
over adjoining rows not thus treated. At Chico, Cal., an increase 
of 129 per cent in the number of pods resulted. Although greater 
seed yields also result, two experiments at least indicate that the 
increase in the number of seeds is not in as high proportion as is 
the increase in the number of pods. 
Further experiments and more exact observations under vary- 
ing conditions in different sections will be necessary to deter- 
mine just when sufficiently increased yields of seed may be ex- 
pected to justify the expense of the undertaking. Any alfalfa seed 
producer may test this method experimentally on a small seale, 
