ag^il'irrrv 



','4. 





4 



f . 



, t , 



Plate IV 



No. 8 Squash of tip of bean root which had been grown in medium containing 

 P^-, prepared by Dr J. R. Pelc, and reproduced with his kind permission. 

 X 2000 (reduction 7/10). (a) Intermitotic nucleus (left) and metaphase 

 chromosomes (right) Feulgen staining, (b) Autoradiograph of same field, 

 focused at level of silver grains, which reveal the presence of P^-. The isotope 

 had been incorporated in both nuclei, probably in the form of nucleoproteins. 



