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 b ag 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.) 



