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30 BULLETIN 75, U. 8. DEFARTMENT OF AGRICULTURE. _ 
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 lies in propagating such bees as are effective pollinators. It 
might, indeed, be profitable to introduce into the United States the 
bees that are most effective in the native land of alfalfa. 
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 which at Chico, Cal., 
formed pods readily and apparently as well as in the open are shown 
in Table XXI. 
TaBLe XX1I.—Species of annual inedicagos readily forming pods under cover of cages. 




Plant designation. | Species. || Plant designation. | Species. 
S. P. I. No. 10725.......| Medicago orbicularis. Bobs Nola 1183-025 i Medicago tuberculata. 
S. P. I. No. 19433........ M. hispida confinis. S. P. I. No. 26077.......| M. scutellata. 
S. P. I. No. 22649......., M. hispida denticulata. | S. P. I. No. 28790.......| M. tuberculata aculeata. 
S. P. I. No. 19449....... | M. turbinata. } S. P. I. No. 9743........| M. muricata. 
S.P.I \| 
I] 
- No. 19442.....-. | M. rugosa. 
Whether 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 in 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 8. 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, containing 28 flowers, were artificially tripped, resulting in three 
pods forming. 
Four racemes, containing 21 flowers, were left untripped as a check, and these set 
one pod. 
The number 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. 
