SWEET-CLOVER SEED. 



13 



was the open check, 4.3 per cent more flowers set seed than on the 

 racemes where the same toothpick was used to spring all the keels, 

 but 11.57 per cent more seed was obtained than in experiment C. 

 Spontaneous self-pollination occurs to only a very small extent, as 

 will be seen from the results of experiment A, in which an average of 

 only 2.9 per cent of the flowers set seed. 



Table III. — Effect of different types of artificial manipulation on the seed production 

 of sweet clover at Arlington, Va., and at Ames, Iowa, in 1916. 



Location. 



Experi- 

 ment. 



Total number of — 



Racemes. 



Flowers. 



Flowers that set 

 seed (per cent). 



At each 

 station. 



Average. 



Arlington 

 Ames 



Arlington 

 Ames 



Arlington 

 Ames 



Arlington 

 Ames 



Arlington 

 Ames 



Arlington 



100 

 196 



3,510 

 4,536 



5,599 

 1,276 



1,229 

 289 



1,480 



575 



377 

 175 



933 



144 

 92 



3,973 

 600 



701 

 133 



936 

 342 



4.1 

 2.0 



70. 95 

 47.02 



57. 03 

 46.02 



63.24 



59.47 



81.43 

 45.71 



2.9 

 66.51 

 54.94 

 62.18 

 70.10 



SEED PRODUCTION OF MELILOTUS ALBA UNDER ORDINARY FIELD 



CONDITIONS. 



The production of seed of Melilotus alba under ordinary field con- 

 ditions varies considerably, not only in different parts of the country 

 but also on different fields in the same region. A number of factors 

 contribute to this variation, one of the most important of which 

 appears to be the inability of the plant to supply all the developing 

 seed with sufficient moisture, causing some of them to abort. As 

 pointed out on page 22 this condition was very marked in certain 

 parts of the country in 1916. However, poor seed production is 

 not always correlated with lack of moisture, for the seed crop was a 

 failure in 1915, where cloudy and rainy weather prevailed much of 

 the time the plants were in bloom. It is believed that the lack of 

 pollination by insects was the principal cause for the failure of seed to 

 set, as very few insects visit sweet-clover flowers when such condi- 

 tions prevail. As sweet-clover pollen will germinate in pure water 

 and as plants which have their roots submerged in water set seed 

 abundantly when pollinated, the failure of the seed crop in 1915 was 

 not due to excessive moisture. 



As a rule, thin stands of sweet clover produce more seed to the 

 acre than thick stands and isolated plants more seed than those 

 growing in either a thick or thin stand. The correlation of seed 



