6 



BULLETIN 75, V. S. DEPARTMENT OF A.GRICULTUBE. 



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-poUinated 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- 

 poUinated 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. — Resultsof naturalandof artificial pollination of alfalfa, at Manhattan, Kans., 



by Roberts and Freeman. 





Method of 

 pollina- 

 tion. 



Weight 

 of stems 

 (grams). 



Num- 

 ber of 

 stems. 



Num- 

 ber of 

 pods. 



Pods producing 

 seeds. 



Number of seeds. 



Plant. 



Num- 

 ber. 



Per 

 cent. 



Pro- 

 duced. 



Average 

 per pod. 



Per 10 



grams 



weight of 



plant. 



Ko. 29. 



/Insects. . . 

 \Hand.... 

 /Insects... 

 \Hand.... 

 /Insects. - . 

 \Hand.... 

 /Insects. . . 

 \Hand.... 

 /Insects... 

 \Hand.... 



/Insects. . . 

 \Hand.... 



49.87 

 35.63 

 103. 88 

 114.00 

 28.50 

 37.00 

 85.50 

 64.13 

 14.00 

 14.00 



11 

 9 

 12 

 18 

 8 

 20 

 11 

 8 

 6 

 8 



255 

 272 

 327 

 279 

 239 

 608 

 449 

 779 

 198 

 311 



30 

 12 

 91 



164 

 65 



103 



228 

 57 

 67 



180 



11.76 

 4.41 

 27.82 

 58.77 

 27.19 

 16.94 

 50.78 

 7.30 

 33.83 

 57.87 



61 



14 



164 



236 



67 



128 



451 



70 



96 



239 



2.03 

 1.17 

 1.80 

 1.44 

 1.03 

 1.24 

 1.96 

 1.22 

 1.43 

 1.32 



12.2 



No. 38 



15.7 



No. 97 



20.7 

 23.5 

 34.6 

 52.7 



No. 98 



No. 109 



68.5 

 170.7 





Summary 



281. 75 

 264. 76 



48 

 63 



1,468 

 2,249 



481 

 516 



32.76 

 22.49 



839 



687 



1.74 

 1.33 



29.7 

 25.9 



Brand and Westgate^ give a brief discussion of the relation of 

 insects to the production of alfalfa seed. These authors assert that 

 "insect 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. 8. Department of Agriculture, Bureau of Plant Industry, Circular 24, 23 p., 3 fig., 1909. 



