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 Diacrisia 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^ 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 
