6 
BULLETIN 104, U. S. DEPARTMENT OF AGRICULTURE. 
(2) Inasmuch as they consume large quantities of pollen, do they thus work injury 
to beets? 
(3) Do they injure the floral organs of beet flowers? 
To be effective agents in the fertilization of beet flowers, they must 
do more than convey pollen from one flower to another on the same 
spike, stem, or plant; they must bring about true cross-pollination. 
Although already late in the season when the foregoing observa- 
tions were made, experiments were at once planned to ascertain 
whether pollination and fertilization might be effected through the 
agency of thrips. To this end several vigorous seed beets, still in 
bloom, were selected. On August 7 
and 8, 1911, the largest buds en a 
number of spikes were emasculated, 
the smaller and more immature buds 
being trimmed off. This work was 
done at the stage when the sepals 
were just about to separate at the 
tips and disclose a tiny yellow spot 
of the anthers, and it was performed 
under a pollinating tent in order to 
exclude flying insects and wind- 
carried pollen (fig. 4 ) . As each set of 
buds was emasculated it was at once 
covered with a white manila paper 
bag, 4 by 6 inches in size. A tuft of 
absorbent cotton was first wrapped 
carefully about the spike some 
inches below the buds. The bag was 
then drawn over the spike until the 
emasculated buds were situated in- 
side the bag near the top, while the 
mouth of the bag reached well below 
the buds and came in contact with 
the wrapping of cotton. The mouth of the bag was then folded diagon- 
ally in such a manner as to pinch the cotton-wrapped stem in one 
corner; then it was folded a second time to make tight contact. 
Metal clips were finally set along the edge of the double fold to secure 
it (fig. 5). The stems bearing these spikes were tied to stakes to 
prevent too much movement and to keep them in an upright posi- 
tion. Before covering the spikes a close search was made for thrips 
or other small insects, any such being removed. The stigmata of 
these flowers became receptive three days later. Thrips were then 
collected from other beet flowers into small vials. As each lot was 
collected it was immediately transferred to one of the bagged spikes. 
Fig. 4.— Pollinating tent of white sheeting, 
which may be completely closed and secured 
with hooks and eyes or buttons. (Original.) 
