SWEET-CLOVER SEED. 15 



of this cage was to determine whether the partial shading of the 

 plants in the cages covered with cheesecloth would have any effect 

 upon the setting of seed. 



The cage covered with wire netting having 14 meshes to the linear 

 inch was used to determine the efficiency as pollinators of sweet 

 clover of insects so small that they could pass through openings of 

 this size. 



The plants used in the experiments at Arlington were growing 

 close to the center of a field of sweet clover. Volunteer plants in a 

 field that contained only a scattering stand were used at Ames. The 

 cages were placed over the plants in all of these experiments before 

 any of the flowers opened, and the work was continued until they 

 were through blooming. 



PLANTS SUBJECT TO INSECT VISITATION AT ALL TIMES. 



A plant subject to insect visits at all times and growing in the same 

 plat as those inclosed in the cages at Arlington was selected as a 

 check to those inclosed in the cages during their entire flowering 

 period or for only a portion of it. This plant, which was in bloom at 

 the same time as those inclosed in the cages, produced 196 racemes 

 with an average of 20.4 pods each. As all of the racemes were col- 

 lected and as those on the lower portions of the plant were smaller 

 than those on the upper branches, the average number of seeds per 

 raceme is much lower than it would have been if only the larger 

 racemes had been collected. 



An isolated plant that was subject to insect visits at all times was 

 selected for a check to the cage work conducted at Ames. This was 

 necessary in order to get results that would be comparable with those 

 obtained from the plants inclosed in the cages, as the cage experi- 

 ments at Ames were conducted with isolated plants. The plant pro- 

 duced 239 racemes, with an average of 41.6 pods. 



PLANTS PROTECTED FROM INSECT VISITATION DURING THEIR ENTIRE FLOWERING 



PERIOD. 



On July 3, 1916, a cage 3 feet square and 3§ feet high, covered with 

 cheesecloth, was placed over three sweet-clover plants at Arlington. 

 (Fig. 6.) This cage was not opened until August 3, when practically 

 all of the racemes had passed the flowering stage and the few seeds 

 that formed on some of them were practically mature. The three 

 plants inclosed in the cage produced 904 racemes, with an average 

 of 0.63 pod each. No pods were produced on 594 racemes, while 150 

 produced but one each. None of the racemes produced more than 

 five pods. 



