ALFALFA SEED PRODUCTION. 23 
the tip of the keel while the flower remained untripped. This proves 
that a pod may develop from a flower without the flower having 
been tripped. The further evidence obtained in this investigation, 
however, indicates that it is only in rare instances that untripped 
alfalfa flowers produce seed. 
In some seasons the alfalfa plants in the fields about Chinook, 
Mont., produce seed in abundance, though honey-gathering insects 
are present in only very small numbers. In other seasons most of 
the flowers fall off the plants without producing pods and seed, and 
only light seed crops are harvested. On August 22, 1910, it was 
found that practically all flowers that had been open for more than 
a few hours had been tripped and that during a period of 10 days 
or 2 weeks prior to this time a very large proportion of the flowers 
had developed into pods. A typical raceme was found to have on 
it 20 flowers which had been opened. Of this number 15 had become 
tripped. The 5 flowers not tripped were newly opened, all being 
located near the top of the raceme. For several days the weather 
had been bright and warm, though not excessively hot. On this 
date flowers just beginning to open were inclosed in netting tents 
and, were watched in order to determine what was causing the flowers 
to become tripped. At this time, however, the weather became 
much colder, a heavy frost occurring on the night of August 24. 
After the weather became colder comparatively few flowers were 
tripped or produced pods. Of a total number of 390 marked flowers 
inside netting tents, only 1 became tripped; of 333 marked flowers 
on plants not inclosed ingnetting, only 3 became tripped. Practically 
all of the flowers that opened after August 22 fell off the plants with- 
out producing pods. Since honey-gathering insects were compara- 
tively rare in the alfalfa fields during the warm weather prior to 
August 22, it seems evident that a large proportion of the flowers 
were becoming automatically tripped and that when the weather 
became colder conditions were no longer favorable for the flowers to 
become tripped and produce seed. 
From the evidence presented, there can be no question that auto- 
matic tripping does occur in alfalfa flowers. It also indicates that in 
rare cases pods form without the flower becoming tripped. 
The evidence also shows that atmospheric or climatic conditions 
greatly affect automatic tripping, so that it is not improbable that this 
factor alone accounts for a great variation in seed production during 
different seasons at the same place. . 
In 1913 it was found at Arlington farm that alfalfa flowers could 
readily be tripped by focusing sunlight upon them with a burning 
glass. The tripping takes place without any evident wilting. 
At Brookings, S. Dak., in 1913, R. A. Oakley observed that when 
the flowers in the shade near the ground were carefully raised into 
