346 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



reflected in the fact that one-half of the terminal leaf had a lower depo- 

 sition of the radioisotope. 



Figure 7-13 is a P^- autoradiogram of roots of the barley plant illustrat- 

 ing the different abilities of different parts of the root to absorb and trans- 

 locate phosphate [courtesy of H. Wiebe (25)]. In the plant on the left 

 the P^^ was applied several centimeters back of the root tip, as indicated 

 by A, and there was considerable translocation to other parts of the plant. 



Fig. 7-12. Translocation pattern of Fe=^ injected into stem of peanut plant. A, site 

 of injection; B, little activity below site of injection; C, D, more translocation occur- 

 ring on left-hand side of stem ; E, one-half of terminal leaf and leaf on right-hand side 

 of petiole showing lower concentrations than F. 



Also note the tendency for selective accumulation at the root tip B. In 

 the plant on the right the same amount of P^- was applied at the root tip 

 C, and it is clear that much less of the radioisotope was transported to 

 other parts of the plant than when the P^'- was apphed some distance 

 back. 



Bone Growth and Development. A clarification of the process of bone 

 growth was made possible by the autoradiographic studies of Leblond 

 et al. (39) using P'*- in rats. Similar studies using Ca"^ with swine were 

 reported by Comar et al. (40, 41). Figure 7-14 illustrates some of the 

 findings. It can be shown from these autoradiograms and from many 



