20 



BULLETIN 844, U. S. DEPARTMENT OF AGRICULTURE. 



belief, as it is doubtful whether the shading of the flowers on the 

 lower racemes is more than that caused by the cheesecloth. It is 

 probably the lack of pollination that causes this decrease in seed pro- 

 duction on the lower branches of plants growing close together, as a 

 vast number of flowers open each day on portions of the plants which 

 are exposed directly to visitation by insects and are therefore more 

 accessible to them. 



In order to obtain information upon the number of flowers that 

 produce seed on the upper and lower portions, respectively, of sweet- 

 clover plants when grown under field conditions and where the stand 

 contained four to five plants to the square foot, a number of racemes 

 were labeled on different portions of the plants at Ames in 1915 and 

 1916. When the pods were partly mature, records were made of the 

 number of flowers that produced pods. The results obtained are 

 given in Table VI. 



Table VI. 



-Relation of the position of sweet-clover flowers on the plants to seed pro- 

 duction, at Ames, Iowa, in 1915 and 1916. 





Position of the flowers. 



Number 



of 

 flowers. 



Pods formed. 



Year. 



Number. 



Percent- 

 age. 



Average. 



1915 





S12 

 261 



344 

 216 



357 

 101 



44 

 59 



43.9 

 38.7 



12.7 

 27.3 



1 42.6 

 | 18. 3 



1916 



do 



1915 



1916 



Lower half of plants 



do 



The flowers on the upper racemes of the plants produced 31.2 per 

 cent more pods than those on the lower racemes in 1915, and 11.4 per 

 cent more in 1916. These results prove that insects more frequently 

 visit the flowers that are directly exposed and are therefore more 

 accessible. 



INFLUENCE OF THE WEATHER AT BLOSSOMING TIME UPON SEED 



PRODUCTION. 



The seed production of sweet clover is seldom satisfactory when 

 rainy or muggy weather prevails during the flowering period. In 

 order to obtain data as to the relation existing between the visits of 

 insects and the prevailing weather conditions, a record of insect visits 

 and of the number of flowers that opened each day was kept for a 

 period of nine days at Ames in August, 1915. 



In this experiment the racemes were marked early each morning 

 just above the last flowers which had opened the previous day, and 

 early the following morning the number of flowers which had opened 

 the previous day was noted. The number of flowers that were polli- 

 nated was determined by the number of pods that formed. Table 

 VII gives in detail the results obtained. 



