16 



THE CURLY-TOP OF BEETS. 



from one side and the edge of the cover raised. The hoops of iron 

 rod are especially useful for cages, covers, etc., and may readily be 

 made by bending lengths of the rod over the edge of a board that 

 has been cut to the proper size and shape, as shown in figure 6. It 

 will be noted that the sides of this board are convergent. This is 

 done to take up the resilience of the iron rod; otherwise the hoops 

 would straddle too much. 



In cages 1 and 2 a standard strain of beet seed was sown on July 

 18, and more on August 4. This germinated and grew under isola- 

 tion conditions. Red 

 spiders and aphides 

 were excluded, but a 

 few thrips gained en- 

 trance through the soil. 

 Cage 1 was carefullv 



CD « 



partitioned into three 

 insect-proof chambers. 

 Colonies of thrips were 

 introduced into cham- 

 ber a; into b six adult 

 beet leaf hoppers were 

 placed, and into c red 

 spiders from the beets 

 in the open field. 

 Aphides Ay ere placed 

 on beets in cage 3. 

 Cage 2 was reserved as 

 a " control." This was 

 done on August 25; 

 from that time the rec- 

 ord of cage 1 is as fol- 

 lows : 



Four more 



Fig. 6.- 



A simple method of preparing iron hoops for 



cages, etc. 



August 2S. 

 placed in b. 



September 7. (a) Plants 

 made good growth: leaves 

 dark green, many of inner ones badly distorted, some being " savoyed " and 

 some cup shaped by thrips' attacks, (b) Scarcely any growth made; leaves 

 dull, leathery, and somewhat blotched or faintly mottled when seen by trans- 

 mitted light; some leaves strongly concave; no vein symptoms, (c) Condi- 

 tions similar to a. 



September S. Placed a few more hoppers in b. 



September 12. (6) Four of the earliest sprouting seedlings show some curl 

 on margin of inner leaves. 



September 17. (b) Several more hoppers introduced. One leaf completely 

 curled. 

 181 



