152 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



Also, the upward slant of the hole causes the isotope to be concentrated 

 in the regions from which it is most readily translocated. 



Miscellaneous Methods with Plants. A typical procedure for studies 

 of ion absorption with excised barley roots of high capacity for ion accu- 

 mulation has been described by Epstein and Hagen (42) . Twenty grams 

 of barley seed was suspended in 10 per cent H2O2 for 20 mm, the H2O2 

 solution then decanted, and the seeds soaked for 24 hr in 1 liter of contin- 

 uously aerated distilled water. After several rinsings they were planted 

 on cheesecloth supported by a stainless-steel screen about 2 cm above the 

 surface of a solution of 10"^ M CaS04. The corners of the cheesecloth 

 were dipped into the solution. Another screen was placed on top of the 

 seeds and covered with cheesecloth which also dipped into the solution. 

 The solution was continuously aerated, and the seedlings were grown m 

 the dark at 24°C. At 44 hr after planting, the top screen was removed, 

 and at 72 hr the solution was renewed, at which time the roots were dipped 

 into distilled water at 24°C. The roots were then removed and blotted 

 on dry cheesecloth, and 1.00-g portions were placed in pyrex test tubes, 

 250 by 22 mm, containing 50 ml of distilled water at 24°C. Each tube 

 was equipped with a 3-mm aerating tube held in place by nonabsorbent 

 cotton. Just prior to the start of the experiment, the water was decanted 

 and replaced by distilled water. The tubes were transferred to a 30°C 

 water bath, the aerators were connected, and the solutions of salts and 

 radioactivity were added. After 3 hr the solutions were decanted, and 

 the roots rinsed with distilled water and prepared for measurement of 

 radioactivity. The standardization of conditions yielded excellent repro- 

 ducibility in the absorption values. 



Pollen of Douglas fir was labeled by Colwell (43) with P^^ m order to 

 study spore distribution patterns. Three methods were compared: dip- 

 ping of basal ends of male cone-bearing branches into P^- solution; direc^t 

 soaking of pollen grains in P^'^ solution; and soaking of pollen grains with 

 alternate application and release of suction. The latter procedure was 

 found to be the best, and the results indicated that the distribution char- 

 acteristics were unaffected by the labeling treatment. 



Soil, Plant, and Fertilizer Methods. Conventional greenhouse or pot 

 techniques are entirely satisfactory provided that care is taken to prevent 

 the spread of contamination. In studies utilizing nutrient solutions there 

 are usually no difficulties, since the radioisotope can be uniformly mixed 

 for presentation to the root surfaces. Figure 4-24 shows a typica 

 arrangement in which the roots of the peanut plant were held m 4-gal 

 glazed crocks, whereas the fruiting zone was maintained separately m 

 sand in an asphaltum-coated metal pan (44) . A complete nutrient solu- 

 tion was applied to each zone, and it was possible to study the relative 

 absorption and distribution of radiocalcium by the root and the fruit. 



