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 faU 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 in«netting, 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 aKalf a 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 carefuUy raised into 



