421S MUTATION AND PLANT BREEDING 



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Figure 1. — Nuclei of root tip cells of Vicia faba that have been grown in 

 tritiated 2-aminopurine for 8 hours. A and B show labeled metaphase 

 chromosomes 24 hours after removal from the base analogue solution. 

 C shows labeled (left) and unlabeled (right) resting nuclei after 48 hours 

 of recovery. 



technique. The slides were then dipped in photographic emulsion 

 and exposed for 12 days. The 24-hour recovery period slides showed 

 evidence of tritium decay in a number of metaphase chromosomes 

 (Figure 1, A and B) and some resting nuclei. After 48 hours of recov- 

 ery few metaphase chromosomes appeared labeled, but many resting 

 nuclei were (Figure 1, C). Some of the label is observed in the cyto- 

 plasm. These observations are tentatively interpreted to indicate 



