30 



BULLEim 75, U. S. DEPAETMENT OF AGKICULTUBE. 



rows. It may be practicable to utilize some simple type of machine 

 that will artificially trip alfalfa flowers and thus increase the seed 

 crop. This subject is at present under investigation. Another pos- 

 sibility hes in propagating such bees as are effective polUnators. It 

 might, indeed, be profitable to introduce into the United States the 

 bees that are most effective in the native land of aKalfa. 



TRIPPING IN RELATION TO SEED SETTING IN ANNUAL MEDICAGOS. 



To determine the relation of tripping by insects to seed setting in 

 the annual medicagos, a number of the species were covered by cages 

 so made as to exclude all but very minute insects and left through 

 the flowering and fruiting period. The species w^hich at Chico, Cal., 

 formed pods readily and apparentlv as well as in the open are shown 

 in Table XXI. 



Table XXI. — Species of annual medicagos readily forming pods under cover of cages. 



Plant designation. 



Species. 



Plant designation. 



Species. 



S. P. I. No. 10725 



S. P. I. No. 19433 



S. P. I. No. 22649 



S. P. I. No. 19449 



S. P. I. No. 19442 



Medicago orbicularis. 

 M. hispida confinis. 

 M. hispida denticulata. 

 M. turbinata. 

 M. rugosa. 



S. P. I. No. 17783 



S. P. I. No. 26077 



S. P. I. No. 28790 



S.P.I. No. 9743 



Medicago tuberculata. 

 M. scutellata. 

 M. tuberculata aculeata. 

 M. muricata. 



Wliether the flowers in any of these species set seed without trip- 

 ping can not be stated positively, but so far as could be determined 

 they became tripped before setting seed, and apparently the tripping 

 was automatic. However, this point could not be determined defi- 

 nitely m all cases. The flowers in some of the species have a very 

 short stamineal column. This makes it difficult to observe the trip- 

 ping process as readily as in species with a long stamineal column. 



In two species (S. P. I. No. 30111, Medicago ciliaris, and S. P. I. 

 No. 16874, Medicago echinus) pods did not form in as large numbers 

 inside the cages as outside, but even with these a number of pods 

 formed in the cages. 



To determine whether artificial tripping is beneficial in Medicago 

 echinus, flowers of this species were worked as follows : 



Six racemes, contaiaing 28 flowers, were artificially tripped, resulting in three 

 pods forming. 



Four racemea, containing 21 flowers, were left iintripped as a check, and these set 

 one pod. 



The nimiber of racemes rather than the number of flowers should 

 be used as a basis of comparison, as not all of the flowers ever set pods. 



In Medicago echinus there are five to seven flowers in a cluster, but 

 only one or two burs form from this number, even though all the 

 flowers in a cluster are tripped. 



