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 obtained. 
Repeated field observations in lowa 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 foealies agree closely with those of Pammel and ie G2), 
who state that barnblebe polimate 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. 289) 
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. 
