THRIPS AS POLLINATORS OF BEET FLOWEES. 



To accomplish this a slit was made in one side of the bag at least 2 

 inches below the buds of the inclosed spike, so that no pollen or thrips 

 might fall upon the flowers when the vial was inverted over the slit, 

 and the pollen-bearing thrips were jarred downward into the bag. 

 This being done, the slit was closed with adhesive plaster, leaving 

 the inclosed thrips free to seek the nectar and distribute the pollen 

 they carried. About 25 

 thrips were put in each bag. 

 Three forms of control or 

 checks were employed at 

 this time: 



(1) Spikes of emasculated buds 

 were isolated, as above described, 

 and left undisturbed. 



(2) Similar spikes were isolated, 

 and when the inclosed flowers had 

 become receptive, slits were made 

 in the bag and at once closed 

 without introducing thrips. 



(3) Spikes of buds were pre- 

 pared as for emasculation and iso- 

 lated without that operation being 

 performed. These also were then 

 left undisturbed. 



One month later, all the 

 bags were opened to exam- 

 ine the inclosed flowers'. 

 The time had been too brief 

 for the maturation of seed, 

 but it was ample for fertil- 

 ization and for the develop- 

 ment of seed to the milky 

 stage. The results were as 

 follows : 



Fig. 5.— Spikes of beet flowers isolated by means of paper 

 bags, showing the method of admitting pollen-bearing 

 thrips through an opening. (Original.) 



Every flower on the checks remained sterile, the sepals of some remaining green. 

 In other cases the entire flower had withered (PI. Ill, fig. 2). Among those to which 

 thrips had been introduced, one set of flowers was lost; of a second set, 16.66 per cent 

 of the flowers became fertilized and produced seed; a third showed 20 per cent of 

 fertilization; and a fourth, 28.6 per cent. For the entire set, the percentage of effec- 

 tive pollination by thrips was 20.37 (PL III, fig. 1). 



On August 26, 1911, eight spikes of wild-beet flowers were similarly 

 treated. Three of these were used as checks. Thrips were placed 

 with the others in the manner above described. Some of these spikes 

 were afterwards broken off, but of those remaining none of the checks 

 became fertilized; of those to which thrips had been admitted only 

 one remained, and 20.5 per cent of its flowers had been fertilized and 

 produced seed. 



