6 BULLETIN 75, U. S. DEPARTMENT OF AGRICULTURE. 
differences were observed among individual plants as regards seed 
production. Of seven plants which showed marked differences in 
this respect, five were classified as “strong” and two as ‘‘ weak.” 
When these plants were inclosed in screens to exclude pollinating 
insects the same tendencies remained evident, two of the plants 
producing pods and seeds in much greater numbers than the others. 
In a second series of plants inclosed in screens and self-pollinated 
by hand the percentage of pods to flowers pollinated varied on differ- 
ent plants from 5.5 per cent to 65.4 per cent, and in one exceptional 
instance 115 per cent. In this last case some flowers evidently 
formed pods without hand pollination. A single plant was inclosed 
in a wire cage to exclude insects. On one half the stems the flowers 
were self-pollinated by hand and produced 97 pods containing 118 
seeds. The other half, not hand pollinated, produced 37 pods con- 
taining 59 seeds. 
In another experiment the investigators inclosed one half of each 
of five plants in a screen cage, leaving the other half exposed to natural 
conditions of pollination. The flowers inclosed in the cage were self- 
pollinated by hand; those outside the cage were naturally pollinated, 
but not necessarily cross-pollinated by insects, as assumed. The 
results they obtained are shown in Table I. <A remarkable feature 
is the extraordinarily large proportion of sterile pods recorded. 
TaBLe I.—Results of natural and of artificial pollination of alfalfa, at Manhattan, Kans., 
by Roberts and Freeman. 






Pods producing 
sends. Number of seeds. 
Method of} Weight | Num- | Num- 
Plant. pollina- | of stems | ber of | ber of Per 10 
tion. (grams). | stems. | pods. Pro- |Average] grams 
duced. | per pod. | weight of 
plant 
No. 29 Insects... 49. 87 11 255 61 2.03 12.2 
BAUS hls mos Basia bia Hand. 35. 63 9 272 14 1.17 3.9 
No. 28 Insects. 103. 88 12 327 164 1. 80 15.7 
SEIS o sap taecl oo Hand.. 114. 00 18 279 236 1. 44 20.7 
No. 97 Insects. 28. 50 8 239 67 1.03 2a50 
HAGA 23 GBS Se Hand.. 37. 00 20 608 128 1. 24 34.6 
No. 98 Insects 85. 50 ll 449 451 1. 96 52.7 
bul dass 33335593506 Hand. 64.13 8 779 70 1. 22 10.9 
No. 109 Insects 14.00 6 198 96 1. 43 68.5 
EEE IS OB Ooo Hand 14. 00 8 311 239 1.32 170.7 
: Insects...} 281.75 48] 1,468 839 1.74 29.7 
Summary. ---- (Hand. 264. 76 63 | 2,249 687} 1.33 25.9 


Brand and Westgate: give a brief discussion of the relation of 
insects to the production of alfalfa seed. These authors assert that 
‘Snsect visitors are essential to the proper pollination of the alfalfa 
flower.”” They state that bumblebees are the most efficient of all 
insects in tripping the flowers and hence bring about pollination. 

1 Brand, C.J.,and Westgate,J.M. Alfalfa in cultivated rows for seed production in semiarid regions. 
U.S. Department of Agriculture, Bureau of Plant Industry, Circular 24, 23 p., 3 fig., 1909. 
