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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



above-described isolation tents do not prevent cross pollination. 

 Separate flowering stems isolated with paper bags generally re- 

 mained completely sterile, though occasionally a few flowers pro- 

 duced seed. Thrips can readily pass through the meshes of any of 

 the above-mentioned fabrics, carrying beet pollen with them. The 



Fig. I. Sketch of a single mesh, greatly enlarged, of three samples of fabric used 

 by German beet seed growers to isolate seed beets to prevent cross pollination. The 

 dot in each mesh represents a beet pollen grain enlarged to the same extent. (C) repre- 

 sencs also the fabric used by the writer. 



writer has recently shown that wind-borne pollen sifts through 

 the tops of tents made of LL sheeting, of 64 threads to the inch, 

 this being the most closely woven fabric used. It is much more 

 closely woven than most of the fabrics used by European beet 

 breeders. 



Apparently the only available method of isolating beets under 

 normal conditions is to plant individual mother beets so remote 

 from each other as to prevent cross pollination by wind or insects. 

 A wind varying from 15 to 30 miles an hour will carry beet pollen 

 over fields of alfalfa to a distance of 400 feet, but the writer was 

 unable to discover any pollen at twice that distance. To be safe 

 from cross pollination by insects a distance of probably two miles 

 is necessary. In early experiments to isolate beets by distance it 

 was not found possible to plant beets two miles away from each 

 other and from garden beets grown by farmers. However this 

 was possible at Jerome, Idaho, in 1913. In the early spring of 

 that year a seed beet was planted at each of eight farms separated 

 from each other by at least two miles, in a locality where it was 



