SWEET-CLOVER SEED. 17 



is 0.11 seed to the raceme less than the average results obtained from 

 the six plants that were covered with cheesecloth. As this difference 

 is well within the limit of variation for individual plants, it may be 

 stated that the shading of the plants in the cheesecloth-covered cages 

 did not reduce the production of seed. The results of this experiment 

 show that spontaneous self-pollination does not occur regularly, as 

 stated by Kirchner. 



FLOWERS POLLINATED ONLY BY NIGHT-FLYING INSECTS. 



In order to determine the importance of night-flying insects as 

 pollinators, two cheesecloth-covered cages 3 feet square and 3§ feet 

 high were placed over sweet-clover plants at Arlington on July 10, 

 1916. The covers of the cages were removed each evening at 7:30 

 and replaced each morning at 4:30 o'clock. Practically all the 

 flowers on these plants had bloomed by August 2, and the seed pro- 

 duced was nearly mature. The few racemes that contained opened 

 flowers or buds were discarded. The three plants in one cage pro- 

 duced 723 racemes, with an average of 3.76 pods each, while the one 

 plant in the other cage produced 227 racemes, with an average of 

 3.58 pods to the raceme. The four plants, therefore, produced a 

 total of 950 racemes, with an average of 3.71 pods each. The only 

 night-flying insect found working on sweet clover while these plants 

 were in bloom was Diaxrisia virginica Fabr. 



This experiment was duplicated at Ames in August, 1916, with the 

 result that one plant subject to visitation only by night-flying insects 

 produced 486 racemes, with an average of 16.5 pods each. 



The results obtained in these experiments show that night-flying 

 insects were much more active in pollinating sweet clover at Ames 

 than at Arlington. However, as the results obtained from the plants 

 subject to visitation by day-flying insects only were practically the 

 same as those obtained from plants which were subject to insect 

 visitation at all times, it is concluded that night-flying insects were 

 not a factor in the pollination of sweet clover at Arlington or at Ames 

 in 1916. 



FLOWERS POLLINATED ONLY BY DAY-FLYING INSECTS. 



A cheesecloth-covered cage, 3 feet square and 3 h feet high, was 

 placed on July 7, 1916, over two sweet-clover plants at Arlington, 

 before any of the flowers opened. As the cover of this cage was 

 removed at 7.30 a. m. and replaced at 4.30 p. m. each day during the 

 experiment, the plants were subject to visitation by day-flying 

 insects only. As soon as all of the flowers on most of the racemes had 

 bloomed, and before any mature pods shattered, the racemes were 

 removed from the plants and the pods produced hj each raceme 

 counted. The two plants produced a total of 544 racemes, with an 

 average of 20.9 pods each. 



153321°— 20— Bull. 844 3 



