12 BULLETIN 75, U. S. DEPARTMENT OF AGRICULTURE. 
ripped flowers beartng pods_¢ 223250 17a ie = eee ea per cent.. 58.06 
Flowers not tripped when inclosed bearing pods. ............. doen 5526 
Average number of seeds per pod from tripped flowers............... ae! 
Average number oi seeds per pod from flowers not tripped when in- 
rol (1s 2.6 Ree pee ON fae NR As WMO NOAA,, URANO T Selb oye | icpetaibe Pig aca fa meh Es 1.00 
The abundant data presented in Table II permit the following con- 
clusions: 
(1) Flowers not tripped either artificially or by insects may produce pods. The 
percentage of pods to flowers under these conditions varies from 11.63 to 0, the aver- 
age for 77 plants being 5.55. 
(2) Flowers artificially tripped produce pods in percentages ranging from 25. 33 to 
44.57, the average for 9,074 flowers on 77 plants being 30.68. 
(3) Under natural sonatiiene the percentage of flowers setting pods varies from 9.24 
to 43.75. The average percentage of pods from 8,939 flowers on 77 plants is 16.76. 
(4) The number of seeds per pod in artificially tripped flowers is usually less than 
in naturally fertilized flowers, the average number of seeds per pod for 77 plants being 
1.72 in the former case and 2.22 in the latter. In caged plants not tripped either 
artificially or by insects the pods averaged 1.78 seeds each. The larger number of 
seeds per pod in the exposed portions of the plants is perhaps due to cross-pollination. 
RELATION OF INSECTS TO TRIPPING. 
To obtain data on the efficiency of insects in tripping alfalfa flowers, 
observations have been made at Pullman, Wash.; Chinook and 
Havre, Mont.; Chico, Cal.; and at Arlington farm, Virginia. No at- 
tempt was made to secure a list of visiting species, the object being 
rather to ascertain the relation, if any, of insect visitors to seed forma- 
tion. 
BEES. 
Among the commonest insects which visit alfalfa flowers are honey- 
gathering bees. The data from detailed observations made at Pull- 
man, Wash., and Chinook and Havre, Mont., are shown in Table IV. 
TasBLe 1V.—Alfalfa flowers tripped by different honey-gathering bees. 






Total Flowers tripped. 
Year. Species. Where observed. tite | 
| visited. | Number. | Per cent. 
[ESE ADRES PEP tees Png wR a ON OADM Oe a Nie PE ey peor et db | 
1909... . pre perner ongtisr ee a ate aoe ae Washes, 30 coe) 318 1 | 0.31 
ADIOS 2 2 GO rss os a ee ce ee fe ees aaine See Oa eee ey ee 189 | 3. 1.58 
HOOD EH DE aes - COXO Rei ae edie ds at se ae eee: Chinook, Mon theese eros 126 6 | 4.76 
1O09mma ly Bomlbus'Sppsb-o sce foes ote aoe Havre, Mout.2 sie oats 268 | 79 29. 47 
1909....| Megachile latimanus.............. Pullman, -Washi-. -s2os.<s252 52 | 47 90.38 
TT (7s es 1 ars sale a ee es ee Chinook: Montes) S22. Jes | 45 | 42| - 93.33 
| 
1 Four species of Bombus were found tripping flowers at Havre, viz, B. awricomus Robertson, B. sepa- 
ratus Cresson, B. bifarius Cresson, B. borealis Kirby. 
It will be noted that the leaf-cutting bee ( Megachile latumanus Say) 
is by far the most efficient, tripping about nine flowers out of every 
ten visited. Bumblebees are decidedly inferior to Megachile, tripping 
