18 BULLETIN 289, U. S. DEPARTMENT OF AGRICULTURE. 



heads were mature. An area 4 feet square was marked off in this 

 cage as -soon as the clover was mature. From this area all heads 

 were collected, kept separate, and thrashed by hand. Of the 311 

 heads collected from this area an average of 30.4 seeds per head 

 was ob tamed. 



Repeated field observations in Iowa in 1911 and 1912 showed that 

 bumblebees were actively engaged in collecting nectar from eight to 

 nine hours a day. Little work was done by them before the dew had 

 entirely disappeared from the foliage and flowers or after 6 o'clock 

 in the evening. Observations showed that bumblebees are able to 

 pollinate 30 to 35 flowers a minute. However, they seldom visit 

 more than eight to ten on a single head at one time. 



These results agree closely with those of Pammel and King (32), 

 who state that bumblebees pollinate on an average 30 flowers a 

 minute, and Smith, according to Beal (3), who estimates from counts 

 that old bees will visit 35 flowers a minute and young bees seldom 

 more than eight. 



HONEYBEES AS CROSS-POLLINATORS OF RED CLOVER. 



The ability of the honeybee to cross-pollinate red clover has been 

 discussed by scientific investigators and beekeepers for some time. 

 Those who do not believe that the honeybee is. able to pollinate red 

 clover base their statements for the most part on the fact that the 

 proboscis of the honeybee is not long enough to reach the nectar 

 located at the base of the staminal tube. Some investigators and 

 bee men state that some strains of the Italian race of honeybees are 

 able to obtain some nectar from red-clover flowers, while other 

 investigators say that honeybees collect pollen from red-clover 

 flowers and thereby cross-pollinate them. 



According to Knuth (22, v. 2, p. 289) the proboscis of the honeybee 

 is 6 mm. in length, which is 3.6 mm. shorter than the average length 

 of the corolla tubes of first-crop red-clover flowers. Honeybees may 

 be able at times to obtain some nectar from the sides of the staminal 

 tubes of red-clover flowers when a large amount is secreted or when 

 the flowers are not in an upright position. Knuth (22, v. 2, p. 2S9) 

 observes that Bombus terrestris, a species of bumblebee found in 

 Europe, pierces the tubes of clover flowers and that honeybees later 

 obtain nectar through these slits. Bombus terrestris has a proboscis 

 from 7 to 9 mm. in length. While working on the experiments 

 reported upon in this bulletin several corolla tubes were observed 

 which had been slit at the base, but it can not be stated that these 

 slits were made by bees. Schneck (34) states that the Virginia car- 

 penter bee (Xylocopa virginica) slits the lower end of the corolla 

 tubes of red-clover flowers and that he has observed honeybees 

 obtaining nectar through the slits. 



