SWEET-CLOVER SEED. 



19 



Table V. — Summary of the insect pollination studies conducted at Arlington, Va., and 



Ames, Iowa, in 1916. 





Num- 

 ber of 

 plants. 



Method of treatment. 



Number of- 





Location. 



Racemes. 



Pods 



pro- 

 duced. 



Pods per 

 raceme, 

 average. 





1 



1 

 3 

 12 

 3 



1 



1 

 2 

 1 

 9 



Check— subject to insect visitation at 



all times. 

 do 



196 



239 



904 



2,370 



723 



227 



486 



544 



418 



1,594 



4, 013 



9,943 



577 



653 



2,720 



152 



8,024 



11,397 



17, 186 



502 



20.47 





41.60 







.63 





do 



- .27 





Visited by night-flying insects only 



(cage 1). 

 Visited by night-flying insects only 



(cage 2). 



Visited by night-flying insects only 



Visited by day-flying insects only 



do 



3.76 



Do ~.. 



.67 





16.51 





20.95 





41.11 



Do 





.31 









The results in Table V show that an average of 0.37 pod to the 

 raceme was obtained from the plants protected from visitation by all 

 insects during the -flowering period. As the racemes of Melilotus 

 alba will average approximately 50 flowers each, less than 1 per cent 

 of them set seed without being pollinated by insects. The results 

 obtained in the cages in which only night-flying insects had access to 

 the flowers show that these insects pollinate sweet clover to a slight 

 extent, but that the number of pods produced by them is so few that 

 it may be assumed that these flowers would have been pollinated by 

 day-flying insects. This assumption is borne out by the results 

 obtained in the cages where only day-flying insects had access to the 

 flowers, as the results obtained in these cages at Arlington and Ames, 

 respectively, are approximately the same as those obtained on the 

 plants subject to insect visitation at all times. It will be noted that 

 the yield of seed on the plants visited by insects at Ames is much 

 higher than that of the plants subjected to insect visits during the 

 same period at Arlington. This difference in seed yield may be 

 attributed to the fact that isolated plants were used in the experi- 

 ments at Ames, and at Arlington the experiments were conducted 

 with plants growing under field conditions. 



RELATION OF THE POSITION OF THE FLOWERS ON MELILOTUS ALBA 

 PLANTS TO SEED PRODUCTION. 



Observations of sweet-clover plants grown under cultivation, and 

 especially when the stands were thick, showed that the flowers of the 

 racemes on the upper and exposed branches produced a larger per- 

 centage of seed than those on the lower branches which were less 

 exposed. It is thought by some that the failure of the flowers on the 

 lower racemes to be fertilized is due to shading; but the results ob- 

 tained in the cheesecloth and glass covered cages do not warrant this 



