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 collected 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 experiments at Ames were conducted with isolated plants. The plant produced 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 3½ 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.
This experiment was duplicated at Ames in August, 1916, with the result that the three protected plants produced a total of 776 racemes, with an average of 0.19 pod each.
