HANDLING OF RADIOISOTOPES WITH ANIMALS AND PLANTS 



151 



Viol, with 

 thread wick 



The tube is filled with solution, care having been taken to wet the cut end 

 of the leafstalk and to expel all air from the rul)bcr tubing. With plants 

 that have grooved leafstalks this method is inapplicable, and the cut end 

 of the stalk must be bent over for submergence in a reservoir. 



Shoot-tip Injection. The tip of the shoot is cut off, and the cut end is 

 kept wet with the liquid. The cut should be made far enough from the 

 growing point to permit access of solution to the differentiated conducting 

 tissues. If the shoot is stiff, it is convenient to use a rubber comiection 

 and reservoir as described for the apple leafstalk. If not, the shoot can 

 be bent over for submergence in a 

 reservoir. 



Stem or Branch Injection. Introduc- 

 tion of solutions into the stem or branch 

 may be accomplished as indicated in 

 Fig. 4-23. A small vial is attached to 

 the stem by tape, and the radioactive 

 solution placed therein. An ordinary 

 sewing needle attached to a heavy 

 thread is passed through the stem, the 

 needle removed, and both ends of the 

 thread immersed in the solution. The 

 solution moves into the plant by capil- 

 lary action. Of course, it is difficult to 

 know just which transport systems are 

 making contact with the thread. How- 

 ever, the results are indicative of trans- 

 port in the plant uncomplicated by 

 considerations of root absorption. 



Branches may be injected independently of the rest of the tree through 

 suitably placed diametrical holes. Trees may also be injected through 

 single diametrical holes or multiple radial holes (40). Graham (40a) 

 has described a convenient techniciue for introduction of radioactive solu- 

 tions into tree stems. The radioactivity contained in 1 ml solution is 

 placed in a shell vial 25 mm long with a 12-mm outside diameter, which is 

 then stoppered with a No. 3 cork of 14-mm diameter at the larger end. 

 At the desired location on the tree trunk or branch, a 13-mm hole is bored 

 with a slight upward slant to a depth of 50 mm. The vial is placed in the 

 hole and its cork firmly seated. A dissecting needle is forced through the 

 center of the cork and the vial is pushed off the cork inside the tree. The 

 needle is withdrawn, with care being taken to hold the cork in place. The 

 cork and surrounding area are immediately covei'ed with a sealing sub- 

 stance such as a 1 : 1 mixture of grafting wax and mineral oil. An advan- 

 tage is that handling of the radioisotopes can be done in the laboratory. 



Fig. 4-23. Method for injoftion of 

 radioactive solution into plant stem. 



